Re: [PATCH] Remove some obfuscation from ${arch}_skip_prologue functions

Yao Qi
2014-09-04T08:59:11Z

Doug Evans <dje@google.com> writes:

> 1) There's no need to call find_pc_partial_function before
> calling skip_prologue_using_sal: The first thing skip_prologue_using_sal
> does is call find_pc_partial_function!

Nowadays we have:

if (find_pc_partial_function (pc, NULL, &func_addr, NULL))
{
CORE_ADDR post_prologue_pc
= skip_prologue_using_sal (gdbarch, func_addr);

if (post_prologue_pc != 0)
return max (pc, post_prologue_pc);
}

so your statement is valid if PC equals to FUNC_ADDR. I don't have a
case that PC and FUNC_ADDR are different, but I'd like to add an assert
to check this, in each target's implementation of skip_prologue hook, or
in the callers of gdbarch_skip_prologue, something like:

if (find_pc_partial_function (pc, NULL, &func_addr, NULL))
gdb_assert (pc == func_addr);

Note that this assert is triggered on arm in
gdb.cp/re-set-overloaded.exp, that is PC is [1] but FUNC_ADDR is [2].

(gdb) disassemble _ZN1CC1Ei
Dump of assembler code for function _ZN1CC1Ev:
0x0000090c <+0>: ldr r12, [pc, #4] ; 0x918 <_ZN1CC1Ev+12> <- [2]
0x00000910 <+4>: add r12, r12, pc
0x00000914 <+8>: bx r12
0x00000918 <+12>: ; <UNDEFINED> instruction: 0xffffffc5
0x0000091c <+0>: ldr r12, [pc, #4] ; 0x928 <_ZN1CC1Ei+12> <- [1]
0x00000920 <+4>: add r12, r12, pc

AFAICS, PC is still the function address but find_pc_partial_function
computes the FUNC_ADDR incorrectly and it is nothing wrong about your
patch.

> nios2: yao@codesourcery.com

I tested your patch on nios2-linux, and no regression is found.

> tic6x:yao@codesourcery.com

My c6x board is dead in data center, so I can't test this patch for it.

--
Yao (齐尧)