linker: avoid -O0 memset while clearing temp_tcb

With -O0, on arm64, Clang uses memset for this declaration:

    bionic_tcb temp_tcb = {};

arm64 doesn't currently have an ifunc for memset, but if it did, then this
line would crash when the linker is compiled with -O0. It looks like other
architectures would only use a memset call if the bionic_tcb struct were
larger.

Avoid memset by using a custom memclr function that the compiler optimizes
into something efficient.

Also add __attribute__((uninitialized)) to ensure that
-ftrivial-auto-var-init does not generate a call to memset. See this
change[1] in build/soong.

[1] If085ec53c619e2cebc86ca23f7039298160d99ae

Test: build linker with -O0, linker[64] --help works
Bug: none
Change-Id: I0df8065a362646de4fa021cae63a7d68ca3966b6

0 files changed, 0 insertions, 0 deletions