* [Qemu-devel] [PATCH] target-sparc: fix 32-bit truncation in fpackfix, avoid undefined behavior
@ 2015-11-06 15:50 Paolo Bonzini
2015-11-06 16:10 ` Richard Henderson
2015-11-06 16:28 ` Mark Cave-Ayland
0 siblings, 2 replies; 3+ messages in thread
From: Paolo Bonzini @ 2015-11-06 15:50 UTC (permalink / raw)
To: qemu-devel; +Cc: Blue Swirl, peter.maydell, Mark Cave-Ayland, armbru, rth
This is reported by Coverity. The algorithm description at
ftp://ftp.icm.edu.pl/packages/ggi/doc/hw/sparc/Sparc.pdf suggests
that the 32-bit parts of rs2, after the left shift, is treated
as a 64-bit integer. Bits 32 and above are used to do the
saturating truncation.
Use a cast to unsigned in order to placate ubsan for negative
inputs, and do so in the other fpack* instructions too.
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
target-sparc/vis_helper.c | 9 ++++++---
1 file changed, 6 insertions(+), 3 deletions(-)
diff --git a/target-sparc/vis_helper.c b/target-sparc/vis_helper.c
index 383cc8b..a1c3343 100644
--- a/target-sparc/vis_helper.c
+++ b/target-sparc/vis_helper.c
@@ -404,7 +404,8 @@ uint32_t helper_fpack16(uint64_t gsr, uint64_t rs2)
for (byte = 0; byte < 4; byte++) {
uint32_t val;
int16_t src = rs2 >> (byte * 16);
- int32_t scaled = src << scale;
+ /* The cast to unsigned avoids undefined behavior for negative src. */
+ int32_t scaled = (uint32_t)src << scale;
int32_t from_fixed = scaled >> 7;
val = (from_fixed < 0 ? 0 :
@@ -426,7 +427,8 @@ uint64_t helper_fpack32(uint64_t gsr, uint64_t rs1, uint64_t rs2)
for (word = 0; word < 2; word++) {
uint64_t val;
int32_t src = rs2 >> (word * 32);
- int64_t scaled = (int64_t)src << scale;
+ /* The cast to unsigned avoids undefined behavior for negative src. */
+ int64_t scaled = (uint64_t)src << scale;
int64_t from_fixed = scaled >> 23;
val = (from_fixed < 0 ? 0 :
@@ -447,7 +449,8 @@ uint32_t helper_fpackfix(uint64_t gsr, uint64_t rs2)
for (word = 0; word < 2; word++) {
uint32_t val;
int32_t src = rs2 >> (word * 32);
- int64_t scaled = src << scale;
+ /* The cast to unsigned avoids undefined behavior for negative src. */
+ int64_t scaled = (uint64_t)src << scale;
int64_t from_fixed = scaled >> 16;
val = (from_fixed < -32768 ? -32768 :
--
2.5.0
^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: [Qemu-devel] [PATCH] target-sparc: fix 32-bit truncation in fpackfix, avoid undefined behavior
2015-11-06 15:50 [Qemu-devel] [PATCH] target-sparc: fix 32-bit truncation in fpackfix, avoid undefined behavior Paolo Bonzini
@ 2015-11-06 16:10 ` Richard Henderson
2015-11-06 16:28 ` Mark Cave-Ayland
1 sibling, 0 replies; 3+ messages in thread
From: Richard Henderson @ 2015-11-06 16:10 UTC (permalink / raw)
To: Paolo Bonzini, qemu-devel
Cc: Blue Swirl, peter.maydell, Mark Cave-Ayland, armbru
On 11/06/2015 04:50 PM, Paolo Bonzini wrote:
> This is reported by Coverity. The algorithm description at
> ftp://ftp.icm.edu.pl/packages/ggi/doc/hw/sparc/Sparc.pdf suggests
> that the 32-bit parts of rs2, after the left shift, is treated
> as a 64-bit integer. Bits 32 and above are used to do the
> saturating truncation.
>
> Use a cast to unsigned in order to placate ubsan for negative
> inputs, and do so in the other fpack* instructions too.
>
> Signed-off-by: Paolo Bonzini<pbonzini@redhat.com>
> ---
> target-sparc/vis_helper.c | 9 ++++++---
> 1 file changed, 6 insertions(+), 3 deletions(-)
Reviewed-by: Richard Henderson <rth@twiddle.net>
r~
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [Qemu-devel] [PATCH] target-sparc: fix 32-bit truncation in fpackfix, avoid undefined behavior
2015-11-06 15:50 [Qemu-devel] [PATCH] target-sparc: fix 32-bit truncation in fpackfix, avoid undefined behavior Paolo Bonzini
2015-11-06 16:10 ` Richard Henderson
@ 2015-11-06 16:28 ` Mark Cave-Ayland
1 sibling, 0 replies; 3+ messages in thread
From: Mark Cave-Ayland @ 2015-11-06 16:28 UTC (permalink / raw)
To: Paolo Bonzini, qemu-devel; +Cc: Blue Swirl, peter.maydell, armbru, rth
On 06/11/15 15:50, Paolo Bonzini wrote:
> This is reported by Coverity. The algorithm description at
> ftp://ftp.icm.edu.pl/packages/ggi/doc/hw/sparc/Sparc.pdf suggests
> that the 32-bit parts of rs2, after the left shift, is treated
> as a 64-bit integer. Bits 32 and above are used to do the
> saturating truncation.
>
> Use a cast to unsigned in order to placate ubsan for negative
> inputs, and do so in the other fpack* instructions too.
>
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> ---
> target-sparc/vis_helper.c | 9 ++++++---
> 1 file changed, 6 insertions(+), 3 deletions(-)
>
> diff --git a/target-sparc/vis_helper.c b/target-sparc/vis_helper.c
> index 383cc8b..a1c3343 100644
> --- a/target-sparc/vis_helper.c
> +++ b/target-sparc/vis_helper.c
> @@ -404,7 +404,8 @@ uint32_t helper_fpack16(uint64_t gsr, uint64_t rs2)
> for (byte = 0; byte < 4; byte++) {
> uint32_t val;
> int16_t src = rs2 >> (byte * 16);
> - int32_t scaled = src << scale;
> + /* The cast to unsigned avoids undefined behavior for negative src. */
> + int32_t scaled = (uint32_t)src << scale;
> int32_t from_fixed = scaled >> 7;
>
> val = (from_fixed < 0 ? 0 :
> @@ -426,7 +427,8 @@ uint64_t helper_fpack32(uint64_t gsr, uint64_t rs1, uint64_t rs2)
> for (word = 0; word < 2; word++) {
> uint64_t val;
> int32_t src = rs2 >> (word * 32);
> - int64_t scaled = (int64_t)src << scale;
> + /* The cast to unsigned avoids undefined behavior for negative src. */
> + int64_t scaled = (uint64_t)src << scale;
> int64_t from_fixed = scaled >> 23;
>
> val = (from_fixed < 0 ? 0 :
> @@ -447,7 +449,8 @@ uint32_t helper_fpackfix(uint64_t gsr, uint64_t rs2)
> for (word = 0; word < 2; word++) {
> uint32_t val;
> int32_t src = rs2 >> (word * 32);
> - int64_t scaled = src << scale;
> + /* The cast to unsigned avoids undefined behavior for negative src. */
> + int64_t scaled = (uint64_t)src << scale;
> int64_t from_fixed = scaled >> 16;
>
> val = (from_fixed < -32768 ? -32768 :
Acked-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>
ATB,
Mark.
^ permalink raw reply [flat|nested] 3+ messages in thread
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2015-11-06 15:50 [Qemu-devel] [PATCH] target-sparc: fix 32-bit truncation in fpackfix, avoid undefined behavior Paolo Bonzini
2015-11-06 16:10 ` Richard Henderson
2015-11-06 16:28 ` Mark Cave-Ayland
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