glibc’s own <sys/ptrace.h> should provide this but doesn’t. See
https://sourceware.org/bugzilla/show_bug.cgi?id=22433.
The copy in compat provided it when targeting x86-64 and using glibc.
util/linux/ptracer.cc uses it when targeting both 32-bit x86 and x86-64,
so the compat definition must be made to apply to 32-bit x86 too.
This also provides a #define using the same name as the constant, which
is what glibc’s <sys/ptrace.h> does for other constants.
Bug: crashpad:30
Change-Id: I5a0734a236d1c25398fb69e66f58dfe118658b68
Reviewed-on: https://chromium-review.googlesource.com/765257
Commit-Queue: Mark Mentovai <mark@chromium.org>
Reviewed-by: Joshua Peraza <jperaza@chromium.org>
Linux supports TLS on x86 by allocating slots in the GDT, accessible
via the system calls get/set_thread_area. This allows segment
registers (%gs on x86) to be used to quickly access the TLS.
Previously, we used PTRACE_GETREGSET with the NT_386_TLS regset. This
"register set" provides access to the subarray of the GDT used for TLS.
However, there are multiple slots provided and we don't know which one
is being used by the threading library for the current thread's TLS.
Previously, we were just using the first one, which worked for x86 on
64-bit kernels, but not 32-bit kernels. On 32-bit kernels, the first
slot ended up pointing to the TLS of the main thread.
The authoritative index of the current thread's TLS in the GDT is
given by bits 3-15 of %gs. However, this index cannot be used with
PTRACE_GETREGSET+NT386_TLS because we don't know the location of the
TLS slots in the GDT. PTRACE_GET_THREAD_AREA, however, accepts an
index from the start of the GDT similarly to get/set_thread_area.
Bug: crashpad:30
Change-Id: Ie6dfbdd088c6816fad409812a1a97037d4b38fd7
Reviewed-on: https://chromium-review.googlesource.com/575318
Reviewed-by: Mark Mentovai <mark@chromium.org>
