| Message ID | 1418817762-9727-1-git-send-email-i.palachev@samsung.com |
|---|---|
| State | New |
| Headers | show |
On 17 December 2014 at 12:02, Ilya Palachev <i.palachev@samsung.com> wrote: > According to official standard POSIX.1-2001. pread64 and pwrite64 > should return 0 for zero-length buffers as mentioned at > > http://pubs.opengroup.org/onlinepubs/009695399/functions/read.html > http://pubs.opengroup.org/onlinepubs/009695399/functions/write.html > > Change-Id: Icd66ea29658329fbd5e6461d1def0c78c81d2671 > Signed-off-by: Ilya Palachev <i.palachev@samsung.com> If this is a problem, doesn't it apply to more syscalls than just pread64 and pwrite64 ? -- PMM
On 17.12.2014 15:28, Peter Maydell wrote: > If this is a problem, doesn't it apply to more syscalls than > just pread64 and pwrite64 ? Hi, We were interested in pwrite64/pread64 only since it caused a failure in elfutils (see https://bugzilla.redhat.com/show_bug.cgi?id=1174267). Of course, it applies also to other syscalls. There are the following problems: - Find what syscalls should be changed (check POSIX specification and qemu implementation) - Whether to change them all with "if" statements as for pread64/pwrite64. Or there is some more convenient way? - Find they how to test them all after the change is made (make check?) What do you think about that? Best regards, Ilya Palachev
On 17 December 2014 at 12:56, Ilya Palachev <i.palachev@samsung.com> wrote: > We were interested in pwrite64/pread64 only since it caused a failure in > elfutils (see https://bugzilla.redhat.com/show_bug.cgi?id=1174267). > Of course, it applies also to other syscalls. There are the following > problems: > > - Find what syscalls should be changed (check POSIX specification and qemu > implementation) Well, we should at least fix all the read/write syscalls, so we're consistent. > - Whether to change them all with "if" statements as for pread64/pwrite64. > Or there is some more convenient way? The other possibility would be to make sure that lock_user/unlock_user succeeded for zero length. But that would be a pain to validate because we'd need to check that no other syscall was relying on the "zero length fails" behaviour. So a specific check and early exit is probably easier and better. > - Find they how to test them all after the change is made (make check?) "make check" doesn't really exercise linux-user. Running the ltp tests is usually a more comprehensive test: http://wiki.qemu.org/Testing/LTP -- PMM
diff --git a/linux-user/syscall.c b/linux-user/syscall.c index a41dd43..a08f5ef 100644 --- a/linux-user/syscall.c +++ b/linux-user/syscall.c @@ -8127,6 +8127,10 @@ abi_long do_syscall(void *cpu_env, int num, abi_ulong arg1, arg4 = arg5; arg5 = arg6; } + if (!arg3) { + ret = 0; + break; + } if (!(p = lock_user(VERIFY_WRITE, arg2, arg3, 0))) goto efault; ret = get_errno(pread64(arg1, p, arg3, target_offset64(arg4, arg5))); @@ -8137,6 +8141,10 @@ abi_long do_syscall(void *cpu_env, int num, abi_ulong arg1, arg4 = arg5; arg5 = arg6; } + if (!arg3) { + ret = 0; + break; + } if (!(p = lock_user(VERIFY_READ, arg2, arg3, 1))) goto efault; ret = get_errno(pwrite64(arg1, p, arg3, target_offset64(arg4, arg5)));
According to official standard POSIX.1-2001. pread64 and pwrite64 should return 0 for zero-length buffers as mentioned at http://pubs.opengroup.org/onlinepubs/009695399/functions/read.html http://pubs.opengroup.org/onlinepubs/009695399/functions/write.html Change-Id: Icd66ea29658329fbd5e6461d1def0c78c81d2671 Signed-off-by: Ilya Palachev <i.palachev@samsung.com> --- linux-user/syscall.c | 8 ++++++++ 1 file changed, 8 insertions(+)