Hello Richard,
being mainly a Pascal programmer,
I always jump when I see such constructs:
You change the type of the print_syscall_err parameter to abi_ulong,
with is an unsigned type as the name suggests,
and after you compare it to a signed constant -4096.
This would never work in Pascal, but this is of course C code.
Nevertheless, I tried:
muller@gcc140:~/pas/check$ cat ./test-unsigned-int.c
#include <stdio.h>
int test_is_error (unsigned int u)
{
return (u > -4096);
}
int main ()
{
unsigned int v;
int error_count = 0;
v = (unsigned int) - 3000;
if (test_is_error(v) != 0)
printf("v=-3000 accepted\n");
else
error_count++;
v = (unsigned int) - 5000;
if (test_is_error(v) == 0)
printf("v=-5000 rejected\n");
else
error_count++;
v = (unsigned int) 0xfffffff0;
if (test_is_error(v) != 0)
printf("v=%d accepted\n",v);
else
error_count++;
if (test_is_error(0xffffff00) != 0)
printf("v=%d accepted\n",0xffffff00);
else
error_count++;
return error_count;
}
muller@gcc140:~/pas/check$ gcc -W -o test-unsigned-int test-unsigned-int.c
test-unsigned-int.c: In function ‘test_is_error’:
test-unsigned-int.c:5:13: warning: comparison of integer expressions of
different signedness: ‘unsigned int’ and ‘int’ [-Wsign-compare]
5 | return (u > -4096);
| ^
The results are OK (both for 32 and 64 bit executables),
but is there a cleaner way, which does not generate a warning, to write this?
Adding an explicit typecast to -4096 seems sufficient to silence that warning.
Pierre Muller
Le 16/03/2022 à 06:58, Richard Henderson a écrit :
Errors are not all negative numbers, but only the top 4k.
Reviewed-by: Philippe Mathieu-Daudé <[email protected]>
Signed-off-by: Richard Henderson <[email protected]>
---
linux-user/strace.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/linux-user/strace.c b/linux-user/strace.c
index 2cdbf030ba..f235118fb6 100644
--- a/linux-user/strace.c
+++ b/linux-user/strace.c
@@ -684,12 +684,12 @@ print_ipc(void *cpu_env, const struct syscallname *name,
*/
static bool
-print_syscall_err(abi_long ret)
+print_syscall_err(abi_ulong ret)
{
const char *errstr;
qemu_log(" = ");
- if (ret < 0) {
+ if (ret > -4096) {
errstr = target_strerror(-ret);
if (errstr) {
qemu_log("-1 errno=%d (%s)", (int)-ret, errstr);
