https://sourceware.org/bugzilla/show_bug.cgi?id=29226
--- Comment #3 from Jason Vas Dias <jason.vas.dias at gmail dot com> ---
OK, as root, if I install the binutils-local-debuginfo and
binutils-local-gold debuginfo RPMs, I can do :
$ cd /usr/local/bin
$ mv ld ld.bin
$ echo '#!/bin/bash
/usr/bin/gdb -q --batch-silent -ex 'set breakpoint pending on' -ex 'b
x86_64.cc:6113' -ex run --args /usr/local/bin/ld.bin "$@"
To make gdb load debuginfo for 'ld' and break at the point
in binutils' gold/x86_64.cc where it is about to log the
error message:
template<int size>
void
Target_x86_64<size>::do_calls_non_split(Relobj* object, unsigned int shndx,
section_offset_type fnoffset,
section_size_type fnsize,
const unsigned char*,
size_t,
unsigned char* view,
section_size_type view_size,
std::string* from,
std::string* to) const
{
const char* const cmp_insn = reinterpret_cast<const char*>
(size == 32 ? cmp_insn_32 : cmp_insn_64);
const char* const lea_r10_insn = reinterpret_cast<const char*>
(size == 32 ? lea_r10_insn_32 : lea_r10_insn_64);
const char* const lea_r11_insn = reinterpret_cast<const char*>
(size == 32 ? lea_r11_insn_32 : lea_r11_insn_64);
const size_t cmp_insn_len =
(size == 32 ? sizeof(cmp_insn_32) : sizeof(cmp_insn_64));
const size_t lea_r10_insn_len =
(size == 32 ? sizeof(lea_r10_insn_32) : sizeof(lea_r10_insn_64));
const size_t lea_r11_insn_len =
(size == 32 ? sizeof(lea_r11_insn_32) : sizeof(lea_r11_insn_64));
const size_t nop_len = (size == 32 ? 7 : 8);
// The function starts with a comparison of the stack pointer and a
// field in the TCB. This is followed by a jump.
// cmp %fs:NN,%rsp
if (this->match_view(view, view_size, fnoffset, cmp_insn, cmp_insn_len)
&& fnsize > nop_len + 1)
{
// We will call __morestack if the carry flag is set after this
// comparison. We turn the comparison into an stc instruction
// and some nops.
view[fnoffset] = '\xf9';
this->set_view_to_nop(view, view_size, fnoffset + 1, nop_len);
}
// lea NN(%rsp),%r10
// lea NN(%rsp),%r11
else if ((this->match_view(view, view_size, fnoffset,
lea_r10_insn, lea_r10_insn_len)
|| this->match_view(view, view_size, fnoffset,
lea_r11_insn, lea_r11_insn_len))
&& fnsize > 8)
{
// This is loading an offset from the stack pointer for a
// comparison. The offset is negative, so we decrease the
// offset by the amount of space we need for the stack. This
// means we will avoid calling __morestack if there happens to
// be plenty of space on the stack already.
unsigned char* pval = view + fnoffset + 4;
uint32_t val = elfcpp::Swap_unaligned<32, false>::readval(pval);
val -= parameters->options().split_stack_adjust_size();
elfcpp::Swap_unaligned<32, false>::writeval(pval, val);
}
else
{
if (!object->has_no_split_stack())
/*LINE #6113:*/object->error(_("failed to match split-stack sequence at "
"section %u offset %0zx"),
shndx, static_cast<size_t>(fnoffset));
return;
}
// We have to change the function so that it calls
// __morestack_non_split instead of __morestack. The former will
// allocate additional stack space.
*from = "__morestack";
*to = "__morestack_non_split";
}
AARGH ! The bug does NOT happen when I run ld this way
under GDB - the command works !
That was most unexpected.
I am now going to have to rebuild ld/gold with line 6113 modified to be:
object->error(_("failed to match split-stack sequence at "
"section %u offset %0zx - r10:%c r11:%c fnsize: %u"),
shndx, static_cast<size_t>(fnoffset)
, this->match_view(view, view_size, fnoffset,
lea_r10_insn, lea_r10_insn_len
) ? '1' : '0'
, this->match_view(view, view_size, fnoffset,
lea_r11_insn, lea_r11_insn_len
&& fnsize > 8)
);
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