Re: [PATCH v2 4/5] Allow display of negative offsets in print_address_symbolic()

[Kevin Buettner <kevinb@redhat.com>]

I somehow missed pushing this commit when I pushed the rest of the
series.  It was strange though - that second hunk of the patch was in,
but the first was not.  Moreover, I didn't see an actual commit in master.

Regardless, it should be in now.

Thanks to Tom de Vries for his help in finding this problem.

Kevin

On Wed,  3 Jul 2019 21:55:02 -0700
Kevin Buettner <kevinb@redhat.com> wrote:

> When examining addresses associated with blocks with non-contiguous
> address ranges, it's not uncommon to see large positive offsets which,
> for some address width, actually represent a smaller negative offset.
> Here's an example taken from the test case (using the
> dw2-ranges-func-lo-cold executable):
> 
>     (gdb) x/5i foo_cold
>        0x40110d <foo+4294967277>:	push   %rbp
>        0x40110e <foo+4294967278>:	mov    %rsp,%rbp
>        0x401111 <foo+4294967281>:	callq  0x401106 <baz>
>        0x401116 <foo+4294967286>:	nop
>        0x401117 <foo+4294967287>:	pop    %rbp
> 
> This commit, in conjuction with an earlier patch from this series, causes
> cases like the above to be displayed like this (below) instead:
> 
> (gdb) x/5i foo_cold
>    0x40110d <foo_cold>:	push   %rbp
>    0x40110e <foo-18>:	mov    %rsp,%rbp
>    0x401111 <foo-15>:	callq  0x401106 <baz>
>    0x401116 <foo-10>:	nop
>    0x401117 <foo-9>:	pop    %rbp
> 
> Note that the address of foo_cold is now (due to another patch) being
> displayed as <foo_cold> instead of <foo+BigOffset>.  The subsequent
> lines are shown as negative offsets from foo.
> 
> Disassembly using the "disassemble" command is somewhat affected by
> these changes:
> 
> Before:
> 
> (gdb) disassemble foo_cold
> Dump of assembler code for function foo:
> Address range 0x401120 to 0x40113b:
>    0x0000000000401120 <+0>:	push   %rbp
>    0x0000000000401121 <+1>:	mov    %rsp,%rbp
>    0x0000000000401124 <+4>:	callq  0x401119 <bar>
>    0x0000000000401129 <+9>:	mov    0x2ef1(%rip),%eax        # 0x404020 <e>
>    0x000000000040112f <+15>:	test   %eax,%eax
>    0x0000000000401131 <+17>:	je     0x401138 <foo+24>
>    0x0000000000401133 <+19>:	callq  0x40110d <foo+4294967277>
>    0x0000000000401138 <+24>:	nop
>    0x0000000000401139 <+25>:	pop    %rbp
>    0x000000000040113a <+26>:	retq
> Address range 0x40110d to 0x401119:
>    0x000000000040110d <+-19>:	push   %rbp
>    0x000000000040110e <+-18>:	mov    %rsp,%rbp
>    0x0000000000401111 <+-15>:	callq  0x401106 <baz>
>    0x0000000000401116 <+-10>:	nop
>    0x0000000000401117 <+-9>:	pop    %rbp
>    0x0000000000401118 <+-8>:	retq
> End of assembler dump.
> 
> After:
> 
> (gdb) disassemble foo_cold
> Dump of assembler code for function foo:
> Address range 0x401120 to 0x40113b:
>    0x0000000000401120 <+0>:	push   %rbp
>    0x0000000000401121 <+1>:	mov    %rsp,%rbp
>    0x0000000000401124 <+4>:	callq  0x401119 <bar>
>    0x0000000000401129 <+9>:	mov    0x2ef1(%rip),%eax        # 0x404020 <e>
>    0x000000000040112f <+15>:	test   %eax,%eax
>    0x0000000000401131 <+17>:	je     0x401138 <foo+24>
>    0x0000000000401133 <+19>:	callq  0x40110d <foo_cold>
>    0x0000000000401138 <+24>:	nop
>    0x0000000000401139 <+25>:	pop    %rbp
>    0x000000000040113a <+26>:	retq
> Address range 0x40110d to 0x401119:
>    0x000000000040110d <-19>:	push   %rbp
>    0x000000000040110e <-18>:	mov    %rsp,%rbp
>    0x0000000000401111 <-15>:	callq  0x401106 <baz>
>    0x0000000000401116 <-10>:	nop
>    0x0000000000401117 <-9>:	pop    %rbp
>    0x0000000000401118 <-8>:	retq
> End of assembler dump.
> 
> Note that negative offsets are now displayed without the leading "+".
> Also, the callq to foo_cold is now displayed as such instead of a callq
> to foo with a large positive offset.
> 
> gdb/ChangeLog:
> 
> 	* printcmd.c (print_address_symbolic): Print negative offsets.
> 	(build_address_symbolic): Force signed arithmetic when computing
> 	offset.
> ---
>  gdb/printcmd.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/gdb/printcmd.c b/gdb/printcmd.c
> index 1109cb3046..dce6ab2db9 100644
> --- a/gdb/printcmd.c
> +++ b/gdb/printcmd.c
> @@ -539,7 +539,7 @@ print_address_symbolic (struct gdbarch *gdbarch, CORE_ADDR addr,
>      fputs_filtered ("<", stream);
>    fputs_styled (name.c_str (), function_name_style.style (), stream);
>    if (offset != 0)
> -    fprintf_filtered (stream, "+%u", (unsigned int) offset);
> +    fprintf_filtered (stream, "%+d", offset);
>  
>    /* Append source filename and line number if desired.  Give specific
>       line # of this addr, if we have it; else line # of the nearest symbol.  */
> @@ -679,7 +679,7 @@ build_address_symbolic (struct gdbarch *gdbarch,
>        && name_location + max_symbolic_offset > name_location)
>      return 1;
>  
> -  *offset = addr - name_location;
> +  *offset = (LONGEST) addr - name_location;
>  
>    *name = name_temp;
>  
> -- 
> 2.21.0
>