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[PATCH] gdb/x86: Fix `-Wstrict-overflow' build error in `i387_collect_xsave'
- From: "Maciej W. Rozycki" <macro at mips dot com>
- To: <gdb-patches at sourceware dot org>
- Cc: Andrew Burgess <andrew dot burgess at embecosm dot com>, <gcc at gcc dot gnu dot org>
- Date: Tue, 15 May 2018 15:45:10 +0100
- Subject: [PATCH] gdb/x86: Fix `-Wstrict-overflow' build error in `i387_collect_xsave'
Make `i' defined within `i387_collect_xsave' unsigned, removing a
`-Werror=strict-overflow' compilation error:
.../gdb/i387-tdep.c: In function 'void i387_collect_xsave(const regcache*, int, void*, int)':
.../gdb/i387-tdep.c:1348:1: error: assuming signed overflow does not occur when assuming that (X + c) < X is always false [-Werror=strict-overflow]
i387_collect_xsave (const struct regcache *regcache, int regnum,
^
cc1plus: all warnings being treated as errors
Makefile:1610: recipe for target 'i387-tdep.o' failed
make: *** [i387-tdep.o] Error 1
seen with GCC 5.4.0, a commit 8ee22052f690 ("gdb/x86: Handle kernels
using compact xsave format") regression. While `regnum' can be -1 on
entry to the function, to mean all registers, `i' is only used with
non-negative register numbers.
gdb/
* i387-tdep.c (i387_collect_xsave): Make `i' unsigned.
---
Hi,
I believe this comes from register numbers being retrieved from the
`tdep' structure at run time and therefore making the compiler unable to
statically determine in loop expression processing that the calculations
made on `i' will not cause a signed overflow.
NB the error message pointing at the function definition rather than the
declaration of `i' makes it rather difficult to determine what the actual
cause might be. I just hope it's only a peculiarity of the somewhat older
version of the compiler and it has been fixed since. Could someone from
the GCC mailing list please comment on that?
OK to apply?
Maciej
---
gdb/i387-tdep.c | 7 ++++---
1 file changed, 4 insertions(+), 3 deletions(-)
gdb-i387-collect-xsave-signed-overflow.diff
Index: gdb/gdb/i387-tdep.c
===================================================================
--- gdb.orig/gdb/i387-tdep.c 2018-05-10 22:13:05.000000000 +0100
+++ gdb/gdb/i387-tdep.c 2018-05-13 23:27:46.194412211 +0100
@@ -1354,7 +1354,7 @@ i387_collect_xsave (const struct regcach
gdb_byte *p, *regs = (gdb_byte *) xsave;
gdb_byte raw[I386_MAX_REGISTER_SIZE];
ULONGEST initial_xstate_bv, clear_bv, xstate_bv = 0;
- int i;
+ unsigned int i;
enum
{
x87_ctrl_or_mxcsr = 0x1,