linux-user: Move syscall error detection into safe_syscall_base

The current api from safe_syscall_base() is to return -errno, which is
the interface provided by *some* linux kernel abis.  The wrapper macro,
safe_syscall(), detects error, stores into errno, and returns -1, to
match the api of the system syscall().

For those kernel abis that do not return -errno natively, this leads
to double syscall error detection.  E.g. Linux ppc64, which sets the
SO flag for error.

Simplify the usage from C by moving the error detection into assembly,
and usage from assembly by providing a C helper with which to set errno.

Reviewed-by: Warner Losh <imp@bsdimp.com>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>

1 files changed, 15 insertions, 12 deletions

diff --git a/linux-user/host/x86_64/safe-syscall.inc.S b/linux-user/host/x86_64/safe-syscall.inc.S
index 158225553e..39b64250c3 100644
--- a/linux-user/host/x86_64/safe-syscall.inc.S
+++ b/linux-user/host/x86_64/safe-syscall.inc.S
@@ -19,9 +19,6 @@
          * first argument an 'int *' to the signal_pending flag, the
          * second one the system call number (as a 'long'), and all further
          * arguments being syscall arguments (also 'long').
-         * We return a long which is the syscall's return value, which
-         * may be negative-errno on failure. Conversion to the
-         * -1-and-errno-set convention is done by the calling wrapper.
          */
 safe_syscall_base:
         .cfi_startproc
@@ -35,9 +32,9 @@ safe_syscall_base:
         .cfi_adjust_cfa_offset 8
         .cfi_rel_offset rbp, 0
 
-        /* The syscall calling convention isn't the same as the
-         * C one:
-         * we enter with rdi == *signal_pending
+        /*
+         * The syscall calling convention isn't the same as the C one:
+         * we enter with rdi == &signal_pending
          *               rsi == syscall number
          *               rdx, rcx, r8, r9, (stack), (stack) == syscall arguments
          *               and return the result in rax
@@ -68,24 +65,30 @@ safe_syscall_base:
 safe_syscall_start:
         /* if signal_pending is non-zero, don't do the call */
         cmpl    $0, (%rbp)
-        jnz     1f
+        jnz     2f
         syscall
 safe_syscall_end:
         /* code path for having successfully executed the syscall */
+        cmp     $-4095, %rax
+        jae     0f
         pop     %rbp
         .cfi_remember_state
         .cfi_def_cfa_offset 8
         .cfi_restore rbp
         ret
+        .cfi_restore_state
+
+0:      neg     %eax
+        jmp     1f
 
-1:
         /* code path when we didn't execute the syscall */
-        .cfi_restore_state
-        mov     $-TARGET_ERESTARTSYS, %rax
-        pop     %rbp
+2:      mov     $TARGET_ERESTARTSYS, %eax
+
+        /* code path setting errno */
+1:      pop     %rbp
         .cfi_def_cfa_offset 8
         .cfi_restore rbp
-        ret
+        jmp     safe_syscall_set_errno_tail
         .cfi_endproc
 
         .size   safe_syscall_base, .-safe_syscall_base