https://gcc.gnu.org/bugzilla/show_bug.cgi?id=93492
--- Comment #9 from H.J. Lu <hjl.tools at gmail dot com> --- (In reply to Fangrui Song from comment #7) > > Is -fasynchronous-unwind-tables compatible with -fpatchable-function-entry? > > Apparently the Linux kernel does not care about it. To make it usable in > userspace, we should place .cfi_startproc in a reasonable place. My patch should handle it. > (A more concerning issue is that __patchable_function_entries can be > stripped by -Wl,--gc-sections , as the bug I linked above describes) I opened: https://sourceware.org/bugzilla/show_bug.cgi?id=25490 > #### Interaction with -g1 (line table) My patch doesn't handle this one. Handle this one requires changing DWARF prologue generation. > % clang -g -fpatchable-function-entry=2 a.c -o a # latest clang > % addr2line -e a 0x$(nm a | awk '/ main/{print $1}') > /tmp/c/a.c:1 > > % gcc -g -fpatchable-function-entry=2 a.c -o a > % addr2line -e a 0x$(nm a | awk '/ main/{print $1}') > ??:? > > For M>0, I think it is fine to leave NOPs before the function entry > uncovered by line table information. clang -fpatchable-function-entry=2,1 > layout is the same as #c2, except for a NOP above foo: > > % clang -g -fpatchable-function-entry=2,1 a.c -o a > # or gcc -g -fpatchable-function-entry=2,1 a.c -o a > % addr2line -e a $(nm a | ruby -ane 'print ($F[0].to_i(16)-1).to_s(16) if / > main/') > crtstuff.c:?
