dl_iterate_phdr is used to search for unwind info provided by either
PT_GNU_EH_FRAME or PT_ARM_EXIDX. Most of the code between the two is
the same, so combine them, and factor out what's different into
checkForUnwindInfoSegment.
Details:
- The FrameHeaderCache can now be enabled for ARM EHABI.
- findUnwindSectionsByPhdr now finds the last PT_ARM_EXIDX rather than
the first. There should only be one segment.
- The dso_base and text_segment_length fields of UnwindInfoSections
are now needed for dl_iterate_phdr when using EHABI, to hold the
low and high PC values for a cache entry.
Reviewed By: compnerd, danielkiss, #libunwind, saugustine
Differential Revision: https://reviews.llvm.org/D87880
* When .eh_frame is located using .eh_frame_hdr (PT_GNU_EH_FRAME), the
start of .eh_frame is known, but not the size. In this case, the
unwinder must rely on a terminator present at the end of .eh_frame.
Set dwarf_section_length to UINTPTR_MAX to indicate this.
* Add a new field, text_segment_length, that the FrameHeaderCache uses
to track the size of the PT_LOAD segment indicated by dso_base.
* Compute ehSectionEnd by adding sectionLength to ehSectionStart,
never to fdeHint.
Fixes PR46829.
Differential Revision: https://reviews.llvm.org/D87750
Define a _LIBUNWIND_USE_DL_ITERATE_PHDR macro in config.h when there is
no other unwind info lookup method. Also define a
_LIBUNWIND_USE_DL_UNWIND_FIND_EXIDX macro to factor out
(__BIONIC__ and _LIBUNWIND_ARM_EHABI).
Differential Revision: https://reviews.llvm.org/D86768
Although it works fine with glibc, as currently implemented the
frameheader cache is incompatible with certain platforms with
slightly different locking semantics inside dl_iterate_phdr.
Therefore only enable it when it is turned on explicitly with
a configure-time option.
Differential Revision: https://reviews.llvm.org/D86163
Summary:
This improves unwind performance quite substantially, and follows
a somewhat similar approach used in libgcc_s as described in the
thread here:
https://gcc.gnu.org/ml/gcc/2005-02/msg00625.html
On certain extremely exception heavy internal tests, the time
drops from about 80 minutes to about five minutes.
Subscribers: libcxx-commits
Tags: #libc
Differential Revision: https://reviews.llvm.org/D75954
Ryan Prichard