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rtld: Add a stop indicator to rtld_start to satisfy unwinders on x86_64

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The right unwinding stop indicator should be CFI-undefined PC.
https://dwarfstd.org/doc/Dwarf3.pdf - page 118:
If a Return Address register is defined in the virtual unwind table,
and its rule is undefined (for example, by DW_CFA_undefined), then
there is no return address and no call address, and the virtual
unwind of stack activations is complete.

That is allows gdb and libunwind successfully stop when unwinding stack
from global constructors and destructors.

Reviewed by:		kib
Differential Revision:	https://reviews.freebsd.org/D40794
This commit is contained in:
Dmitry Chagin 2023-07-01 10:51:35 +03:00
parent f85b82daf1
commit 3bdf68086d
1 changed files with 5 additions and 0 deletions
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5
libexec/rtld-elf/amd64/rtld_start.S
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@ -30,14 +30,18 @@
.globl .rtld_start
.type .rtld_start,@function
.rtld_start:
.cfi_startproc
.cfi_undefined %rip
xorq %rbp,%rbp # Clear frame pointer for good form
subq $24,%rsp # A place to store exit procedure addr
.cfi_def_cfa_offset 32
movq %rdi,%r12
movq %rsp,%rsi # save address of exit proc
movq %rsp,%rdx # construct address of obj_main
addq $8,%rdx
call _rtld # Call rtld(sp); returns entry point
popq %rsi # Get exit procedure address
.cfi_def_cfa_offset 24
movq %r12,%rdi # *ap
/*
* At this point, %rax contains the entry point of the main program, and
@ -47,6 +51,7 @@
.globl .rtld_goto_main
.rtld_goto_main: # This symbol exists just to make debugging easier.
jmp *%rax # Enter main program
.cfi_endproc
/*