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

[Kevin Buettner <kevinb@redhat.com>]

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