[PATCH] linux-user: Use "!= 0" when checking if MAP_FIXED_NOREPLACE is non-zero

[PATCH] linux-user: Use "!= 0" when checking if MAP_FIXED_NOREPLACE is non-zero

[Peter Maydell]

In pgd_find_hole_fallback(), Coverity doesn't like the use
of "if (MAP_FIXED_NOREPLACE || ...)" because it's using a
logical operator on a constant other than 0 or 1 and its
heuristic thinks we might have intended a bitwise operator
instead.

The logic is correct (we are checking whether the host really
has a MAP_FIXED_NOREPLACE or whether we fell back to the
"#define as 0 to ignore" from osdep.h); make Coverity
happier by explicitly writing out the comparison with zero.

Fixes: Coverity CID 1431059
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
---
 linux-user/elfload.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/linux-user/elfload.c b/linux-user/elfload.c
index e19d0b5cb05..0b02a926025 100644
--- a/linux-user/elfload.c
+++ b/linux-user/elfload.c
@@ -2188,7 +2188,8 @@ static uintptr_t pgd_find_hole_fallback(uintptr_t guest_size, uintptr_t brk,
                                      PROT_NONE, flags, -1, 0);
             if (mmap_start != MAP_FAILED) {
                 munmap((void *) align_start, guest_size);
-                if (MAP_FIXED_NOREPLACE || mmap_start == (void *) align_start) {
+                if (MAP_FIXED_NOREPLACE != 0 ||
+                    mmap_start == (void *) align_start) {
                     return (uintptr_t) mmap_start + offset;
                 }
             }
-- 
2.20.1

Re: [PATCH] linux-user: Use "!= 0" when checking if MAP_FIXED_NOREPLACE is non-zero

[Philippe Mathieu-Daudé]

On 11/3/20 3:26 PM, Peter Maydell wrote:
> In pgd_find_hole_fallback(), Coverity doesn't like the use
> of "if (MAP_FIXED_NOREPLACE || ...)" because it's using a
> logical operator on a constant other than 0 or 1 and its
> heuristic thinks we might have intended a bitwise operator
> instead.
> 
> The logic is correct (we are checking whether the host really
> has a MAP_FIXED_NOREPLACE or whether we fell back to the
> "#define as 0 to ignore" from osdep.h); make Coverity
> happier by explicitly writing out the comparison with zero.
> 
> Fixes: Coverity CID 1431059
> Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
> ---
>  linux-user/elfload.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)

Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>

Re: [PATCH] linux-user: Use "!= 0" when checking if MAP_FIXED_NOREPLACE is non-zero

[Laurent Vivier]

Le 03/11/2020 à 15:26, Peter Maydell a écrit :
> In pgd_find_hole_fallback(), Coverity doesn't like the use
> of "if (MAP_FIXED_NOREPLACE || ...)" because it's using a
> logical operator on a constant other than 0 or 1 and its
> heuristic thinks we might have intended a bitwise operator
> instead.
> 
> The logic is correct (we are checking whether the host really
> has a MAP_FIXED_NOREPLACE or whether we fell back to the
> "#define as 0 to ignore" from osdep.h); make Coverity
> happier by explicitly writing out the comparison with zero.
> 
> Fixes: Coverity CID 1431059
> Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
> ---
>  linux-user/elfload.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/linux-user/elfload.c b/linux-user/elfload.c
> index e19d0b5cb05..0b02a926025 100644
> --- a/linux-user/elfload.c
> +++ b/linux-user/elfload.c
> @@ -2188,7 +2188,8 @@ static uintptr_t pgd_find_hole_fallback(uintptr_t guest_size, uintptr_t brk,
>                                       PROT_NONE, flags, -1, 0);
>              if (mmap_start != MAP_FAILED) {
>                  munmap((void *) align_start, guest_size);
> -                if (MAP_FIXED_NOREPLACE || mmap_start == (void *) align_start) {
> +                if (MAP_FIXED_NOREPLACE != 0 ||
> +                    mmap_start == (void *) align_start) {
>                      return (uintptr_t) mmap_start + offset;
>                  }
>              }
> 

Applied to my linux-user-for-5.2 branch.

Thanks,
Laurent