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<title>Using the GNU Compiler Collection (GCC): Debugging Options</title>
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<a name="Debugging-Options"></a>
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<p>
Next: <a href="Optimize-Options.html#Optimize-Options" accesskey="n" rel="next">Optimize Options</a>, Previous: <a href="Static-Analyzer-Options.html#Static-Analyzer-Options" accesskey="p" rel="previous">Static Analyzer Options</a>, Up: <a href="Invoking-GCC.html#Invoking-GCC" accesskey="u" rel="up">Invoking GCC</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Indices.html#Indices" title="Index" rel="index">Index</a>]</p>
</div>
<hr>
<a name="Options-for-Debugging-Your-Program"></a>
<h3 class="section">3.10 Options for Debugging Your Program</h3>
<a name="index-options_002c-debugging"></a>
<a name="index-debugging-information-options"></a>
<p>To tell GCC to emit extra information for use by a debugger, in almost
all cases you need only to add <samp>-g</samp> to your other options. Some debug
formats can co-exist (like DWARF with CTF) when each of them is enabled
explicitly by adding the respective command line option to your other options.
</p>
<p>GCC allows you to use <samp>-g</samp> with
<samp>-O</samp>. The shortcuts taken by optimized code may occasionally
be surprising: some variables you declared may not exist
at all; flow of control may briefly move where you did not expect it;
some statements may not be executed because they compute constant
results or their values are already at hand; some statements may
execute in different places because they have been moved out of loops.
Nevertheless it is possible to debug optimized output. This makes
it reasonable to use the optimizer for programs that might have bugs.
</p>
<p>If you are not using some other optimization option, consider
using <samp>-Og</samp> (see <a href="Optimize-Options.html#Optimize-Options">Optimize Options</a>) with <samp>-g</samp>.
With no <samp>-O</samp> option at all, some compiler passes that collect
information useful for debugging do not run at all, so that
<samp>-Og</samp> may result in a better debugging experience.
</p>
<dl compact="compact">
<dd><a name="index-g"></a>
</dd>
<dt><code>-g</code></dt>
<dd><p>Produce debugging information in the operating system’s native format
(stabs, COFF, XCOFF, or DWARF). GDB can work with this debugging
information.
</p>
<p>On most systems that use stabs format, <samp>-g</samp> enables use of extra
debugging information that only GDB can use; this extra information
makes debugging work better in GDB but probably makes other debuggers
crash or refuse to read the program. If you want to control for certain whether
to generate the extra information, use <samp>-gvms</samp> (see below).
</p>
<a name="index-ggdb"></a>
</dd>
<dt><code>-ggdb</code></dt>
<dd><p>Produce debugging information for use by GDB. This means to use the
most expressive format available (DWARF, stabs, or the native format
if neither of those are supported), including GDB extensions if at all
possible.
</p>
<a name="index-gdwarf"></a>
</dd>
<dt><code>-gdwarf</code></dt>
<dt><code>-gdwarf-<var>version</var></code></dt>
<dd><p>Produce debugging information in DWARF format (if that is supported).
The value of <var>version</var> may be either 2, 3, 4 or 5; the default
version for most targets is 5 (with the exception of VxWorks, TPF and
Darwin/Mac OS X, which default to version 2, and AIX, which defaults
to version 4).
</p>
<p>Note that with DWARF Version 2, some ports require and always
use some non-conflicting DWARF 3 extensions in the unwind tables.
</p>
<p>Version 4 may require GDB 7.0 and <samp>-fvar-tracking-assignments</samp>
for maximum benefit. Version 5 requires GDB 8.0 or higher.
</p>
<p>GCC no longer supports DWARF Version 1, which is substantially
different than Version 2 and later. For historical reasons, some
other DWARF-related options such as
<samp>-fno-dwarf2-cfi-asm</samp>) retain a reference to DWARF Version 2
in their names, but apply to all currently-supported versions of DWARF.
</p>
<a name="index-gbtf"></a>
</dd>
<dt><code>-gbtf</code></dt>
<dd><p>Request BTF debug information. BTF is the default debugging format for the
eBPF target. On other targets, like x86, BTF debug information can be
generated along with DWARF debug information when both of the debug formats are
enabled explicitly via their respective command line options.
</p>
<a name="index-gctf"></a>
</dd>
<dt><code>-gctf</code></dt>
<dt><code>-gctf<var>level</var></code></dt>
<dd><p>Request CTF debug information and use level to specify how much CTF debug
information should be produced. If <samp>-gctf</samp> is specified
without a value for level, the default level of CTF debug information is 2.
</p>
<p>CTF debug information can be generated along with DWARF debug information when
both of the debug formats are enabled explicitly via their respective command
line options.
</p>
<p>Level 0 produces no CTF debug information at all. Thus, <samp>-gctf0</samp>
negates <samp>-gctf</samp>.
</p>
<p>Level 1 produces CTF information for tracebacks only. This includes callsite
information, but does not include type information.
</p>
<p>Level 2 produces type information for entities (functions, data objects etc.)
at file-scope or global-scope only.
</p>
<a name="index-gvms"></a>
</dd>
<dt><code>-gvms</code></dt>
<dd><p>Produce debugging information in Alpha/VMS debug format (if that is
supported). This is the format used by DEBUG on Alpha/VMS systems.
</p>
</dd>
<dt><code>-g<var>level</var></code></dt>
<dt><code>-ggdb<var>level</var></code></dt>
<dt><code>-gvms<var>level</var></code></dt>
<dd><p>Request debugging information and also use <var>level</var> to specify how
much information. The default level is 2.
</p>
<p>Level 0 produces no debug information at all. Thus, <samp>-g0</samp> negates
<samp>-g</samp>.
</p>
<p>Level 1 produces minimal information, enough for making backtraces in
parts of the program that you don’t plan to debug. This includes
descriptions of functions and external variables, and line number
tables, but no information about local variables.
</p>
<p>Level 3 includes extra information, such as all the macro definitions
present in the program. Some debuggers support macro expansion when
you use <samp>-g3</samp>.
</p>
<p>If you use multiple <samp>-g</samp> options, with or without level numbers,
the last such option is the one that is effective.
</p>
<p><samp>-gdwarf</samp> does not accept a concatenated debug level, to avoid
confusion with <samp>-gdwarf-<var>level</var></samp>.
Instead use an additional <samp>-g<var>level</var></samp> option to change the
debug level for DWARF.
</p>
<a name="index-feliminate_002dunused_002ddebug_002dsymbols"></a>
<a name="index-fno_002deliminate_002dunused_002ddebug_002dsymbols"></a>
</dd>
<dt><code>-fno-eliminate-unused-debug-symbols</code></dt>
<dd><p>By default, no debug information is produced for symbols that are not actually
used. Use this option if you want debug information for all symbols.
</p>
<a name="index-femit_002dclass_002ddebug_002dalways"></a>
</dd>
<dt><code>-femit-class-debug-always</code></dt>
<dd><p>Instead of emitting debugging information for a C++ class in only one
object file, emit it in all object files using the class. This option
should be used only with debuggers that are unable to handle the way GCC
normally emits debugging information for classes because using this
option increases the size of debugging information by as much as a
factor of two.
</p>
<a name="index-fmerge_002ddebug_002dstrings"></a>
<a name="index-fno_002dmerge_002ddebug_002dstrings"></a>
</dd>
<dt><code>-fno-merge-debug-strings</code></dt>
<dd><p>Direct the linker to not merge together strings in the debugging
information that are identical in different object files. Merging is
not supported by all assemblers or linkers. Merging decreases the size
of the debug information in the output file at the cost of increasing
link processing time. Merging is enabled by default.
</p>
<a name="index-fdebug_002dprefix_002dmap"></a>
</dd>
<dt><code>-fdebug-prefix-map=<var>old</var>=<var>new</var></code></dt>
<dd><p>When compiling files residing in directory <samp><var>old</var></samp>, record
debugging information describing them as if the files resided in
directory <samp><var>new</var></samp> instead. This can be used to replace a
build-time path with an install-time path in the debug info. It can
also be used to change an absolute path to a relative path by using
<samp>.</samp> for <var>new</var>. This can give more reproducible builds, which
are location independent, but may require an extra command to tell GDB
where to find the source files. See also <samp>-ffile-prefix-map</samp>
and <samp>-fcanon-prefix-map</samp>.
</p>
<a name="index-fvar_002dtracking"></a>
</dd>
<dt><code>-fvar-tracking</code></dt>
<dd><p>Run variable tracking pass. It computes where variables are stored at each
position in code. Better debugging information is then generated
(if the debugging information format supports this information).
</p>
<p>It is enabled by default when compiling with optimization (<samp>-Os</samp>,
<samp>-O</samp>, <samp>-O2</samp>, …), debugging information (<samp>-g</samp>) and
the debug info format supports it.
</p>
<a name="index-fvar_002dtracking_002dassignments"></a>
<a name="index-fno_002dvar_002dtracking_002dassignments"></a>
</dd>
<dt><code>-fvar-tracking-assignments</code></dt>
<dd><p>Annotate assignments to user variables early in the compilation and
attempt to carry the annotations over throughout the compilation all the
way to the end, in an attempt to improve debug information while
optimizing. Use of <samp>-gdwarf-4</samp> is recommended along with it.
</p>
<p>It can be enabled even if var-tracking is disabled, in which case
annotations are created and maintained, but discarded at the end.
By default, this flag is enabled together with <samp>-fvar-tracking</samp>,
except when selective scheduling is enabled.
</p>
<a name="index-gsplit_002ddwarf"></a>
</dd>
<dt><code>-gsplit-dwarf</code></dt>
<dd><p>If DWARF debugging information is enabled, separate as much debugging
information as possible into a separate output file with the extension
<samp>.dwo</samp>. This option allows the build system to avoid linking files with
debug information. To be useful, this option requires a debugger capable of
reading <samp>.dwo</samp> files.
</p>
<a name="index-gdwarf32"></a>
<a name="index-gdwarf64"></a>
</dd>
<dt><code>-gdwarf32</code></dt>
<dt><code>-gdwarf64</code></dt>
<dd><p>If DWARF debugging information is enabled, the <samp>-gdwarf32</samp> selects
the 32-bit DWARF format and the <samp>-gdwarf64</samp> selects the 64-bit
DWARF format. The default is target specific, on most targets it is
<samp>-gdwarf32</samp> though. The 32-bit DWARF format is smaller, but
can’t support more than 2GiB of debug information in any of the DWARF
debug information sections. The 64-bit DWARF format allows larger debug
information and might not be well supported by all consumers yet.
</p>
<a name="index-gdescribe_002ddies"></a>
</dd>
<dt><code>-gdescribe-dies</code></dt>
<dd><p>Add description attributes to some DWARF DIEs that have no name attribute,
such as artificial variables, external references and call site
parameter DIEs.
</p>
<a name="index-gpubnames"></a>
</dd>
<dt><code>-gpubnames</code></dt>
<dd><p>Generate DWARF <code>.debug_pubnames</code> and <code>.debug_pubtypes</code> sections.
</p>
<a name="index-ggnu_002dpubnames"></a>
</dd>
<dt><code>-ggnu-pubnames</code></dt>
<dd><p>Generate <code>.debug_pubnames</code> and <code>.debug_pubtypes</code> sections in a format
suitable for conversion into a GDB index. This option is only useful
with a linker that can produce GDB index version 7.
</p>
<a name="index-fdebug_002dtypes_002dsection"></a>
<a name="index-fno_002ddebug_002dtypes_002dsection"></a>
</dd>
<dt><code>-fdebug-types-section</code></dt>
<dd><p>When using DWARF Version 4 or higher, type DIEs can be put into
their own <code>.debug_types</code> section instead of making them part of the
<code>.debug_info</code> section. It is more efficient to put them in a separate
comdat section since the linker can then remove duplicates.
But not all DWARF consumers support <code>.debug_types</code> sections yet
and on some objects <code>.debug_types</code> produces larger instead of smaller
debugging information.
</p>
<a name="index-grecord_002dgcc_002dswitches"></a>
<a name="index-gno_002drecord_002dgcc_002dswitches"></a>
</dd>
<dt><code>-grecord-gcc-switches</code></dt>
<dt><code>-gno-record-gcc-switches</code></dt>
<dd><p>This switch causes the command-line options used to invoke the
compiler that may affect code generation to be appended to the
DW_AT_producer attribute in DWARF debugging information. The options
are concatenated with spaces separating them from each other and from
the compiler version.
It is enabled by default.
See also <samp>-frecord-gcc-switches</samp> for another
way of storing compiler options into the object file.
</p>
<a name="index-gstrict_002ddwarf"></a>
</dd>
<dt><code>-gstrict-dwarf</code></dt>
<dd><p>Disallow using extensions of later DWARF standard version than selected
with <samp>-gdwarf-<var>version</var></samp>. On most targets using non-conflicting
DWARF extensions from later standard versions is allowed.
</p>
<a name="index-gno_002dstrict_002ddwarf"></a>
</dd>
<dt><code>-gno-strict-dwarf</code></dt>
<dd><p>Allow using extensions of later DWARF standard version than selected with
<samp>-gdwarf-<var>version</var></samp>.
</p>
<a name="index-gas_002dloc_002dsupport"></a>
</dd>
<dt><code>-gas-loc-support</code></dt>
<dd><p>Inform the compiler that the assembler supports <code>.loc</code> directives.
It may then use them for the assembler to generate DWARF2+ line number
tables.
</p>
<p>This is generally desirable, because assembler-generated line-number
tables are a lot more compact than those the compiler can generate
itself.
</p>
<p>This option will be enabled by default if, at GCC configure time, the
assembler was found to support such directives.
</p>
<a name="index-gno_002das_002dloc_002dsupport"></a>
</dd>
<dt><code>-gno-as-loc-support</code></dt>
<dd><p>Force GCC to generate DWARF2+ line number tables internally, if DWARF2+
line number tables are to be generated.
</p>
<a name="index-gas_002dlocview_002dsupport"></a>
</dd>
<dt><code>-gas-locview-support</code></dt>
<dd><p>Inform the compiler that the assembler supports <code>view</code> assignment
and reset assertion checking in <code>.loc</code> directives.
</p>
<p>This option will be enabled by default if, at GCC configure time, the
assembler was found to support them.
</p>
</dd>
<dt><code>-gno-as-locview-support</code></dt>
<dd><p>Force GCC to assign view numbers internally, if
<samp>-gvariable-location-views</samp> are explicitly requested.
</p>
<a name="index-gcolumn_002dinfo"></a>
<a name="index-gno_002dcolumn_002dinfo"></a>
</dd>
<dt><code>-gcolumn-info</code></dt>
<dt><code>-gno-column-info</code></dt>
<dd><p>Emit location column information into DWARF debugging information, rather
than just file and line.
This option is enabled by default.
</p>
<a name="index-gstatement_002dfrontiers"></a>
<a name="index-gno_002dstatement_002dfrontiers"></a>
</dd>
<dt><code>-gstatement-frontiers</code></dt>
<dt><code>-gno-statement-frontiers</code></dt>
<dd><p>This option causes GCC to create markers in the internal representation
at the beginning of statements, and to keep them roughly in place
throughout compilation, using them to guide the output of <code>is_stmt</code>
markers in the line number table. This is enabled by default when
compiling with optimization (<samp>-Os</samp>, <samp>-O1</samp>, <samp>-O2</samp>,
…), and outputting DWARF 2 debug information at the normal level.
</p>
<a name="index-gvariable_002dlocation_002dviews"></a>
<a name="index-gvariable_002dlocation_002dviews_003dincompat5"></a>
<a name="index-gno_002dvariable_002dlocation_002dviews"></a>
</dd>
<dt><code>-gvariable-location-views</code></dt>
<dt><code>-gvariable-location-views=incompat5</code></dt>
<dt><code>-gno-variable-location-views</code></dt>
<dd><p>Augment variable location lists with progressive view numbers implied
from the line number table. This enables debug information consumers to
inspect state at certain points of the program, even if no instructions
associated with the corresponding source locations are present at that
point. If the assembler lacks support for view numbers in line number
tables, this will cause the compiler to emit the line number table,
which generally makes them somewhat less compact. The augmented line
number tables and location lists are fully backward-compatible, so they
can be consumed by debug information consumers that are not aware of
these augmentations, but they won’t derive any benefit from them either.
</p>
<p>This is enabled by default when outputting DWARF 2 debug information at
the normal level, as long as there is assembler support,
<samp>-fvar-tracking-assignments</samp> is enabled and
<samp>-gstrict-dwarf</samp> is not. When assembler support is not
available, this may still be enabled, but it will force GCC to output
internal line number tables, and if
<samp>-ginternal-reset-location-views</samp> is not enabled, that will most
certainly lead to silently mismatching location views.
</p>
<p>There is a proposed representation for view numbers that is not backward
compatible with the location list format introduced in DWARF 5, that can
be enabled with <samp>-gvariable-location-views=incompat5</samp>. This
option may be removed in the future, is only provided as a reference
implementation of the proposed representation. Debug information
consumers are not expected to support this extended format, and they
would be rendered unable to decode location lists using it.
</p>
<a name="index-ginternal_002dreset_002dlocation_002dviews"></a>
<a name="index-gno_002dinternal_002dreset_002dlocation_002dviews"></a>
</dd>
<dt><code>-ginternal-reset-location-views</code></dt>
<dt><code>-gno-internal-reset-location-views</code></dt>
<dd><p>Attempt to determine location views that can be omitted from location
view lists. This requires the compiler to have very accurate insn
length estimates, which isn’t always the case, and it may cause
incorrect view lists to be generated silently when using an assembler
that does not support location view lists. The GNU assembler will flag
any such error as a <code>view number mismatch</code>. This is only enabled
on ports that define a reliable estimation function.
</p>
<a name="index-ginline_002dpoints"></a>
<a name="index-gno_002dinline_002dpoints"></a>
</dd>
<dt><code>-ginline-points</code></dt>
<dt><code>-gno-inline-points</code></dt>
<dd><p>Generate extended debug information for inlined functions. Location
view tracking markers are inserted at inlined entry points, so that
address and view numbers can be computed and output in debug
information. This can be enabled independently of location views, in
which case the view numbers won’t be output, but it can only be enabled
along with statement frontiers, and it is only enabled by default if
location views are enabled.
</p>
<a name="index-gz"></a>
</dd>
<dt><code>-gz<span class="roman">[</span>=<var>type</var><span class="roman">]</span></code></dt>
<dd><p>Produce compressed debug sections in DWARF format, if that is supported.
If <var>type</var> is not given, the default type depends on the capabilities
of the assembler and linker used. <var>type</var> may be one of
‘<samp>none</samp>’ (don’t compress debug sections), or ‘<samp>zlib</samp>’ (use zlib
compression in ELF gABI format). If the linker doesn’t support writing
compressed debug sections, the option is rejected. Otherwise, if the
assembler does not support them, <samp>-gz</samp> is silently ignored when
producing object files.
</p>
<a name="index-femit_002dstruct_002ddebug_002dbaseonly"></a>
</dd>
<dt><code>-femit-struct-debug-baseonly</code></dt>
<dd><p>Emit debug information for struct-like types
only when the base name of the compilation source file
matches the base name of file in which the struct is defined.
</p>
<p>This option substantially reduces the size of debugging information,
but at significant potential loss in type information to the debugger.
See <samp>-femit-struct-debug-reduced</samp> for a less aggressive option.
See <samp>-femit-struct-debug-detailed</samp> for more detailed control.
</p>
<p>This option works only with DWARF debug output.
</p>
<a name="index-femit_002dstruct_002ddebug_002dreduced"></a>
</dd>
<dt><code>-femit-struct-debug-reduced</code></dt>
<dd><p>Emit debug information for struct-like types
only when the base name of the compilation source file
matches the base name of file in which the type is defined,
unless the struct is a template or defined in a system header.
</p>
<p>This option significantly reduces the size of debugging information,
with some potential loss in type information to the debugger.
See <samp>-femit-struct-debug-baseonly</samp> for a more aggressive option.
See <samp>-femit-struct-debug-detailed</samp> for more detailed control.
</p>
<p>This option works only with DWARF debug output.
</p>
<a name="index-femit_002dstruct_002ddebug_002ddetailed"></a>
</dd>
<dt><code>-femit-struct-debug-detailed<span class="roman">[</span>=<var>spec-list</var><span class="roman">]</span></code></dt>
<dd><p>Specify the struct-like types
for which the compiler generates debug information.
The intent is to reduce duplicate struct debug information
between different object files within the same program.
</p>
<p>This option is a detailed version of
<samp>-femit-struct-debug-reduced</samp> and <samp>-femit-struct-debug-baseonly</samp>,
which serves for most needs.
</p>
<p>A specification has the syntax<br>
[‘<samp>dir:</samp>’|‘<samp>ind:</samp>’][‘<samp>ord:</samp>’|‘<samp>gen:</samp>’](‘<samp>any</samp>’|‘<samp>sys</samp>’|‘<samp>base</samp>’|‘<samp>none</samp>’)
</p>
<p>The optional first word limits the specification to
structs that are used directly (‘<samp>dir:</samp>’) or used indirectly (‘<samp>ind:</samp>’).
A struct type is used directly when it is the type of a variable, member.
Indirect uses arise through pointers to structs.
That is, when use of an incomplete struct is valid, the use is indirect.
An example is
‘<samp>struct one direct; struct two * indirect;</samp>’.
</p>
<p>The optional second word limits the specification to
ordinary structs (‘<samp>ord:</samp>’) or generic structs (‘<samp>gen:</samp>’).
Generic structs are a bit complicated to explain.
For C++, these are non-explicit specializations of template classes,
or non-template classes within the above.
Other programming languages have generics,
but <samp>-femit-struct-debug-detailed</samp> does not yet implement them.
</p>
<p>The third word specifies the source files for those
structs for which the compiler should emit debug information.
The values ‘<samp>none</samp>’ and ‘<samp>any</samp>’ have the normal meaning.
The value ‘<samp>base</samp>’ means that
the base of name of the file in which the type declaration appears
must match the base of the name of the main compilation file.
In practice, this means that when compiling <samp>foo.c</samp>, debug information
is generated for types declared in that file and <samp>foo.h</samp>,
but not other header files.
The value ‘<samp>sys</samp>’ means those types satisfying ‘<samp>base</samp>’
or declared in system or compiler headers.
</p>
<p>You may need to experiment to determine the best settings for your application.
</p>
<p>The default is <samp>-femit-struct-debug-detailed=all</samp>.
</p>
<p>This option works only with DWARF debug output.
</p>
<a name="index-fdwarf2_002dcfi_002dasm"></a>
<a name="index-fno_002ddwarf2_002dcfi_002dasm"></a>
</dd>
<dt><code>-fno-dwarf2-cfi-asm</code></dt>
<dd><p>Emit DWARF unwind info as compiler generated <code>.eh_frame</code> section
instead of using GAS <code>.cfi_*</code> directives.
</p>
<a name="index-feliminate_002dunused_002ddebug_002dtypes"></a>
<a name="index-fno_002deliminate_002dunused_002ddebug_002dtypes"></a>
</dd>
<dt><code>-fno-eliminate-unused-debug-types</code></dt>
<dd><p>Normally, when producing DWARF output, GCC avoids producing debug symbol
output for types that are nowhere used in the source file being compiled.
Sometimes it is useful to have GCC emit debugging
information for all types declared in a compilation
unit, regardless of whether or not they are actually used
in that compilation unit, for example
if, in the debugger, you want to cast a value to a type that is
not actually used in your program (but is declared). More often,
however, this results in a significant amount of wasted space.
</p></dd>
</dl>
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