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.
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
---
linux-user/safe-syscall.h | 16 +++-------
linux-user/safe-syscall-error.c | 28 ++++++++++++++++
linux-user/host/aarch64/safe-syscall.inc.S | 20 ++++++------
linux-user/host/arm/safe-syscall.inc.S | 27 ++++++++++------
linux-user/host/i386/safe-syscall.inc.S | 37 +++++++++++++++-------
linux-user/host/ppc64/safe-syscall.inc.S | 20 ++++++------
linux-user/host/riscv/safe-syscall.inc.S | 20 ++++++------
linux-user/host/s390x/safe-syscall.inc.S | 32 ++++++++++++-------
linux-user/host/x86_64/safe-syscall.inc.S | 29 +++++++++--------
linux-user/meson.build | 1 +
10 files changed, 145 insertions(+), 85 deletions(-)
create mode 100644 linux-user/safe-syscall-error.c
Note: My s390 assembler skills are quite weak, but it seems consistent with
the rest of the code. I'm less sure about the riscv and ppc64, but am quite
confident in the arm, aarch64, x86 and meson change. Not sure how to otherwise
signal that when the review is uneven.
diff --git a/linux-user/safe-syscall.h b/linux-user/safe-syscall.h
index aaa9ffc0e2..97837faddb 100644
--- a/linux-user/safe-syscall.h
+++ b/linux-user/safe-syscall.h
@@ -127,21 +127,15 @@
#ifdef HAVE_SAFE_SYSCALL
/* The core part of this function is implemented in assembly */
extern long safe_syscall_base(int *pending, long number, ...);
+extern long safe_syscall_set_errno_tail(int value);
+
/* These are defined by the safe-syscall.inc.S file */
extern char safe_syscall_start[];
extern char safe_syscall_end[];
-#define safe_syscall(...) \
- ({ \
- long ret_; \
- int *psp_ = &((TaskState *)thread_cpu->opaque)->signal_pending; \
- ret_ = safe_syscall_base(psp_, __VA_ARGS__); \
- if (is_error(ret_)) { \
- errno = -ret_; \
- ret_ = -1; \
- } \
- ret_; \
- })
+#define safe_syscall(...) \
+ safe_syscall_base(&((TaskState *)thread_cpu->opaque)->signal_pending, \
+ __VA_ARGS__)
#else
diff --git a/linux-user/safe-syscall-error.c b/linux-user/safe-syscall-error.c
new file mode 100644
index 0000000000..d7e2700f81
--- /dev/null
+++ b/linux-user/safe-syscall-error.c
@@ -0,0 +1,28 @@
+/*
+ * safe-syscall-error.c: errno setting fragment
+ * This is intended to be invoked by safe-syscall.S
+ *
+ * Written by Richard Henderson <rth@twiddle.net>
+ * Copyright (C) 2021 Red Hat, Inc.
+ *
+ * This work is licensed under the terms of the GNU GPL, version 2 or later.
+ * See the COPYING file in the top-level directory.
+ */
+
+#include "qemu/osdep.h"
+#include "hostdep.h"
+#include "safe-syscall.h"
+
+#ifdef HAVE_SAFE_SYSCALL
+/*
+ * This is intended to be invoked via tail-call on the error path
+ * from the assembly in host/arch/safe-syscall.inc.S. This takes
+ * care of the host specific addressing of errno.
+ * Return -1 to finalize the return value for safe_syscall_base.
+ */
+long safe_syscall_set_errno_tail(int value)
+{
+ errno = value;
+ return -1;
+}
+#endif
diff --git a/linux-user/host/aarch64/safe-syscall.inc.S b/linux-user/host/aarch64/safe-syscall.inc.S
index e2e726ef55..76a0a18a6c 100644
--- a/linux-user/host/aarch64/safe-syscall.inc.S
+++ b/linux-user/host/aarch64/safe-syscall.inc.S
@@ -22,15 +22,12 @@
* 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
/* The syscall calling convention isn't the same as the
* C one:
- * we enter with x0 == *signal_pending
+ * we enter with x0 == &signal_pending
* x1 == syscall number
* x2 ... x7, (stack) == syscall arguments
* and return the result in x0
@@ -60,16 +57,21 @@ safe_syscall_base:
safe_syscall_start:
/* if signal_pending is non-zero, don't do the call */
ldr w10, [x9]
- cbnz w10, 0f
+ cbnz w10, 2f
svc 0x0
safe_syscall_end:
/* code path for having successfully executed the syscall */
+ cmp x0, #-4096
+ b.hi 0f
ret
-0:
+ /* code path setting errno */
+0: neg w0, w0
+ b safe_syscall_set_errno_tail
+
/* code path when we didn't execute the syscall */
- mov x0, #-TARGET_ERESTARTSYS
- ret
- .cfi_endproc
+2: mov w0, #TARGET_ERESTARTSYS
+ b safe_syscall_set_errno_tail
+ .cfi_endproc
.size safe_syscall_base, .-safe_syscall_base
diff --git a/linux-user/host/arm/safe-syscall.inc.S b/linux-user/host/arm/safe-syscall.inc.S
index 1f1ee8327b..618112c6bf 100644
--- a/linux-user/host/arm/safe-syscall.inc.S
+++ b/linux-user/host/arm/safe-syscall.inc.S
@@ -27,9 +27,6 @@
* 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:
.fnstart
@@ -46,7 +43,7 @@ safe_syscall_base:
.cfi_rel_offset lr, 20
/* The syscall calling convention isn't the same as the C one:
- * we enter with r0 == *signal_pending
+ * we enter with r0 == &signal_pending
* r1 == syscall number
* r2, r3, [sp+0] ... [sp+12] == syscall arguments
* and return the result in r0
@@ -74,17 +71,29 @@ safe_syscall_start:
/* if signal_pending is non-zero, don't do the call */
ldr r12, [r8] /* signal_pending */
tst r12, r12
- bne 1f
+ bne 2f
swi 0
safe_syscall_end:
/* code path for having successfully executed the syscall */
+ cmp r0, #-4096
+ neghi r0, r0
+ bhi 1f
pop { r4, r5, r6, r7, r8, pc }
-1:
/* code path when we didn't execute the syscall */
- ldr r0, =-TARGET_ERESTARTSYS
- pop { r4, r5, r6, r7, r8, pc }
+2: mov r0, #TARGET_ERESTARTSYS
+
+ /* code path setting errno */
+1: pop { r4, r5, r6, r7, r8, lr }
+ .cfi_adjust_cfa_offset -24
+ .cfi_restore r4
+ .cfi_restore r5
+ .cfi_restore r6
+ .cfi_restore r7
+ .cfi_restore r8
+ .cfi_restore lr
+ b safe_syscall_set_errno_tail
+
.fnend
.cfi_endproc
-
.size safe_syscall_base, .-safe_syscall_base
diff --git a/linux-user/host/i386/safe-syscall.inc.S b/linux-user/host/i386/safe-syscall.inc.S
index e425aa54d8..f5883234bb 100644
--- a/linux-user/host/i386/safe-syscall.inc.S
+++ b/linux-user/host/i386/safe-syscall.inc.S
@@ -20,9 +20,6 @@
* 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
@@ -41,7 +38,7 @@ safe_syscall_base:
/* The syscall calling convention isn't the same as the C one:
* we enter with 0(%esp) == return address
- * 4(%esp) == *signal_pending
+ * 4(%esp) == &signal_pending
* 8(%esp) == syscall number
* 12(%esp) ... 32(%esp) == syscall arguments
* and return the result in eax
@@ -70,11 +67,13 @@ safe_syscall_start:
/* if signal_pending is non-zero, don't do the call */
mov 4+16(%esp), %eax /* signal_pending */
cmpl $0, (%eax)
- jnz 1f
+ jnz 2f
mov 8+16(%esp), %eax /* syscall number */
int $0x80
safe_syscall_end:
/* code path for having successfully executed the syscall */
+ cmp $-4095, %eax
+ jae 0f
pop %ebx
.cfi_remember_state
.cfi_adjust_cfa_offset -4
@@ -89,12 +88,28 @@ safe_syscall_end:
.cfi_adjust_cfa_offset -4
.cfi_restore ebp
ret
-
-1:
- /* code path when we didn't execute the syscall */
.cfi_restore_state
- mov $-TARGET_ERESTARTSYS, %eax
- jmp safe_syscall_end
- .cfi_endproc
+0: neg %eax
+ jmp 1f
+
+ /* code path when we didn't execute the syscall */
+2: mov $TARGET_ERESTARTSYS, %eax
+
+ /* code path setting errno */
+1: pop %ebx
+ .cfi_adjust_cfa_offset -4
+ .cfi_restore ebx
+ pop %edi
+ .cfi_adjust_cfa_offset -4
+ .cfi_restore edi
+ pop %esi
+ .cfi_adjust_cfa_offset -4
+ .cfi_restore esi
+ pop %ebp
+ .cfi_adjust_cfa_offset -4
+ .cfi_restore ebp
+ jmp safe_syscall_set_errno_tail
+
+ .cfi_endproc
.size safe_syscall_base, .-safe_syscall_base
diff --git a/linux-user/host/ppc64/safe-syscall.inc.S b/linux-user/host/ppc64/safe-syscall.inc.S
index 5f19cd193c..b370889480 100644
--- a/linux-user/host/ppc64/safe-syscall.inc.S
+++ b/linux-user/host/ppc64/safe-syscall.inc.S
@@ -22,9 +22,6 @@
* 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.
*/
#if _CALL_ELF == 2
safe_syscall_base:
@@ -39,7 +36,7 @@ safe_syscall_base:
.L.safe_syscall_base:
.cfi_startproc
#endif
- /* We enter with r3 == *signal_pending
+ /* We enter with r3 == &signal_pending
* r4 == syscall number
* r5 ... r10 == syscall arguments
* and return the result in r3
@@ -69,19 +66,20 @@ safe_syscall_start:
/* if signal_pending is non-zero, don't do the call */
lwz 12, 0(11)
cmpwi 0, 12, 0
- bne- 0f
+ bne- 2f
sc
safe_syscall_end:
/* code path when we did execute the syscall */
- bnslr+
-
- /* syscall failed; return negative errno */
- neg 3, 3
+ bso- 1f
blr
/* code path when we didn't execute the syscall */
-0: addi 3, 0, -TARGET_ERESTARTSYS
- blr
+2: addi 3, 0, TARGET_ERESTARTSYS
+
+ /* code path setting errno */
+1: b safe_syscall_set_errno_tail
+ nop /* per abi, for the linker to modify */
+
.cfi_endproc
#if _CALL_ELF == 2
diff --git a/linux-user/host/riscv/safe-syscall.inc.S b/linux-user/host/riscv/safe-syscall.inc.S
index 95c4832de2..54c2e23f75 100644
--- a/linux-user/host/riscv/safe-syscall.inc.S
+++ b/linux-user/host/riscv/safe-syscall.inc.S
@@ -23,15 +23,12 @@
* 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
/*
* The syscall calling convention is nearly the same as C:
- * we enter with a0 == *signal_pending
+ * we enter with a0 == &signal_pending
* a1 == syscall number
* a2 ... a7 == syscall arguments
* and return the result in a0
@@ -62,16 +59,21 @@ safe_syscall_base:
safe_syscall_start:
/* If signal_pending is non-zero, don't do the call */
lw t1, 0(t0)
- bnez t1, 0f
+ bnez t1, 2f
scall
safe_syscall_end:
/* code path for having successfully executed the syscall */
+ li t2, -4096
+ bgtu a0, t2, 0f
ret
-0:
+ /* code path setting errno */
+0: neg a0, a0
+ j safe_syscall_set_errno_tail
+
/* code path when we didn't execute the syscall */
- li a0, -TARGET_ERESTARTSYS
- ret
- .cfi_endproc
+2: li a0, TARGET_ERESTARTSYS
+ j safe_syscall_set_errno_tail
+ .cfi_endproc
.size safe_syscall_base, .-safe_syscall_base
diff --git a/linux-user/host/s390x/safe-syscall.inc.S b/linux-user/host/s390x/safe-syscall.inc.S
index d97d27458e..899dab39e9 100644
--- a/linux-user/host/s390x/safe-syscall.inc.S
+++ b/linux-user/host/s390x/safe-syscall.inc.S
@@ -20,9 +20,6 @@
* 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
@@ -44,9 +41,9 @@ safe_syscall_base:
stg %r1,0(%r15) /* store back chain */
stg %r0,8(%r15) /* store eos */
- /* The syscall calling convention isn't the same as the
- * C one:
- * we enter with r2 == *signal_pending
+ /*
+ * The syscall calling convention isn't the same as the C one:
+ * we enter with r2 == &signal_pending
* r3 == syscall number
* r4, r5, r6, (stack) == syscall arguments
* and return the result in r2
@@ -77,14 +74,25 @@ safe_syscall_start:
svc 0
safe_syscall_end:
-1: lg %r15,0(%r15) /* load back chain */
+ /* code path for having successfully executed the syscall */
+ lg %r15,0(%r15) /* load back chain */
.cfi_remember_state
.cfi_adjust_cfa_offset -160
lmg %r6,%r15,48(%r15) /* load saved registers */
- br %r14
- .cfi_restore_state
-2: lghi %r2, -TARGET_ERESTARTSYS
- j 1b
- .cfi_endproc
+ lghi %r0, -4095 /* check for syscall error */
+ clgr %r2, %r0
+ blr %r14 /* return on success */
+ lcr %r2, %r2 /* create positive errno */
+ jg safe_syscall_set_errno_tail
+ .cfi_restore_state
+
+ /* code path when we didn't execute the syscall */
+2: lg %r15,0(%r15) /* load back chain */
+ .cfi_adjust_cfa_offset -160
+ lmg %r6,%r15,48(%r15) /* load saved registers */
+ lghi %r2, TARGET_ERESTARTSYS
+ jg safe_syscall_set_errno_tail
+
+ .cfi_endproc
.size safe_syscall_base, .-safe_syscall_base
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
-
-1:
- /* code path when we didn't execute the syscall */
.cfi_restore_state
- mov $-TARGET_ERESTARTSYS, %rax
- pop %rbp
+
+0: neg %eax
+ jmp 1f
+
+ /* code path when we didn't execute the syscall */
+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
diff --git a/linux-user/meson.build b/linux-user/meson.build
index bf62c13e37..94ac3c58ce 100644
--- a/linux-user/meson.build
+++ b/linux-user/meson.build
@@ -10,6 +10,7 @@ linux_user_ss.add(files(
'main.c',
'mmap.c',
'safe-syscall.S',
+ 'safe-syscall-error.c',
'signal.c',
'strace.c',
'syscall.c',
--
2.25.1