[PATCH v4] target/i386: Fix handling of k_gs_base register in 32-bit mode in gdbstub

[PATCH v4] target/i386: Fix handling of k_gs_base register in 32-bit mode in gdbstub

[Marek Dolata - mkdolata@us.ibm.com]

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Fixes: corrects clobbering of registers appearing after k_gs_base
Buglink: https://bugs.launchpad.net/qemu/+bug/1857640

Signed-off-by: Marek Dolata <mkdolata@us.ibm.com>
---
target/i386/gdbstub.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/target/i386/gdbstub.c b/target/i386/gdbstub.c
index aef25b70f1..572ead641c 100644
--- a/target/i386/gdbstub.c
+++ b/target/i386/gdbstub.c
@@ -350,15 +350,15 @@ int x86_cpu_gdb_write_register(CPUState *cs, uint8_t *mem_buf, int n)
             env->segs[R_GS].base = ldl_p(mem_buf);
             return 4;
-#ifdef TARGET_X86_64
         case IDX_SEG_REGS + 8:
+#ifdef TARGET_X86_64
             if (env->hflags & HF_CS64_MASK) {
                 env->kernelgsbase = ldq_p(mem_buf);
                 return 8;
             }
             env->kernelgsbase = ldl_p(mem_buf);
-            return 4;
#endif
+            return 4;
         case IDX_FP_REGS + 8:
             cpu_set_fpuc(env, ldl_p(mem_buf));
--
2.24.1


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Re: [PATCH v4] target/i386: Fix handling of k_gs_base register in 32-bit mode in gdbstub

[Paolo Bonzini]

On 29/12/19 03:48, Marek Dolata - mkdolata@us.ibm.com wrote:
> Fixes: corrects clobbering of registers appearing after k_gs_base
> Buglink: https://bugs.launchpad.net/qemu/+bug/1857640
> 
> Signed-off-by: Marek Dolata <mkdolata@us.ibm.com>

Queued.  Note that I had to apply the patch by hand since you probably did
some cut-and-paste job.  I also added a meaningful commit message:

    gdb-xml/i386-32bit.xml includes the k_gs_base register too, so we have to
    handle it even if TARGET_X86_64 is not defined.  This is already done in
    x86_cpu_gdb_read_register, but not in x86_cpu_gdb_write_register where the
    incorrect return value causes all registers after it to be clobbered.
    
    Fixes https://bugs.launchpad.net/qemu/+bug/1857640.

Thanks,

Paolo