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Re: [Qemu-arm] [RFC PATCH] target/arm: semihosting docs, formatting and
From: |
Peter Maydell |
Subject: |
Re: [Qemu-arm] [RFC PATCH] target/arm: semihosting docs, formatting and return clean-ups |
Date: |
Mon, 13 May 2019 14:14:34 +0100 |
On Fri, 10 May 2019 at 20:10, Alex Bennée <address@hidden> wrote:
>
> This is a clean-up of the semihosting calls after reading ver 2.0 of
> the specification. There are a number of small fixes that seemed too
> insignificant to split into smaller patches:
>
> - add reference to the ARM semihosting spec
> - add some additional commentary on return values
> - fixup block comments as per standard
> - audit return values, return 0xdeadbeef for corrupted values
> - fix up leaks from early returns with lock_user_string
> - return bytes not written/read instead of -1
> - add LOG_UNIMP for missing functionality
>
> This is very much a Friday patch. It might be worth splitting up if
> coming back for a more concerted clean-up series for semihosting as
> the asynchronous gdb calls probably need more attention.
>
> Signed-off-by: Alex Bennée <address@hidden>
> ---
> target/arm/arm-semi.c | 180 +++++++++++++++++++++++++-----------------
> 1 file changed, 109 insertions(+), 71 deletions(-)
>
> diff --git a/target/arm/arm-semi.c b/target/arm/arm-semi.c
> index 4c326fdc2fb..8deaed2807c 100644
> --- a/target/arm/arm-semi.c
> +++ b/target/arm/arm-semi.c
> @@ -2,6 +2,7 @@
> * Arm "Angel" semihosting syscalls
> *
> * Copyright (c) 2005, 2007 CodeSourcery.
> + * Copyright (c) 2019 Linaro
> * Written by Paul Brook.
> *
> * This program is free software; you can redistribute it and/or modify
> @@ -15,13 +16,19 @@
> * GNU General Public License for more details.
> *
> * You should have received a copy of the GNU General Public License
> - * along with this program; if not, see <http://www.gnu.org/licenses/>.
> + * along with this program; if not, see
> + * <http://www.gnu.org/licenses/>.
> + *
> + * ARM Semihosting is documented in:
> + * Semihosting for AArch32 and AArch64 Release 2.0
> + * https://static.docs.arm.com/100863/0200/semihosting.pdf
> */
>
> #include "qemu/osdep.h"
>
> #include "cpu.h"
> #include "exec/semihost.h"
> +#include "exec/log.h"
> #ifdef CONFIG_USER_ONLY
> #include "qemu.h"
>
> @@ -241,13 +248,18 @@ static target_ulong arm_gdb_syscall(ARMCPU *cpu,
> gdb_syscall_complete_cb cb,
> put_user_u64(val, args + (n) * 8) : \
> put_user_u32(val, args + (n) * 4))
>
> +/*
> + * Do a semihosting call. Returns the "RETURN REGISTER" which is
> + * documented as corrupted for some calls. In this case we use the
> + * venerable 0xdeadbeef.
> + */
I think what you mean here is something like "the specification always
says that the "return register" either returns a specific value or
is corrupted, so we don't need to report to our caller whether we
are returning a value or trying to leave the register unchanged.
We use 0xdeadbeef as the return value when there isn't a defined
return value for the call."
> target_ulong do_arm_semihosting(CPUARMState *env)
> {
> ARMCPU *cpu = arm_env_get_cpu(env);
> CPUState *cs = CPU(cpu);
> target_ulong args;
> target_ulong arg0, arg1, arg2, arg3;
> - char * s;
> + char *s;
> int nr;
> uint32_t ret;
> uint32_t len;
> @@ -273,9 +285,9 @@ target_ulong do_arm_semihosting(CPUARMState *env)
> GET_ARG(2);
> s = lock_user_string(arg0);
> if (!s) {
> - /* FIXME - should this error code be -TARGET_EFAULT ? */
We definitely don't want to return -TARGET_EFAULT, but we could
in theory call set_swi_errno(ts, EFAULT). The spec says that
it's up to the implementation, effectively, so I think I agree
we don't need to bother. Any caller which has messed things up
sufficiently to be passing us bogus memory is unlikely to be
in a state to successfully call SYS_ERRNO anyway.
> return (uint32_t)-1;
> }
> + /* check for invalid open mode */
> if (arg1 >= 12) {
> unlock_user(s, arg0, 0);
> return (uint32_t)-1;
> @@ -287,7 +299,7 @@ target_ulong do_arm_semihosting(CPUARMState *env)
> }
> if (use_gdb_syscalls()) {
> ret = arm_gdb_syscall(cpu, arm_semi_cb, "open,%s,%x,1a4", arg0,
> - (int)arg2+1, gdb_open_modeflags[arg1]);
> + (int) arg2 + 1, gdb_open_modeflags[arg1]);
The space after the cast looks a bit odd here.
> } else {
> ret = set_swi_errno(ts, open(s, open_modeflags[arg1], 0644));
> }
> @@ -301,48 +313,51 @@ target_ulong do_arm_semihosting(CPUARMState *env)
> return set_swi_errno(ts, close(arg0));
> }
> case TARGET_SYS_WRITEC:
> - {
> - char c;
> -
> - if (get_user_u8(c, args))
> - /* FIXME - should this error code be -TARGET_EFAULT ? */
> - return (uint32_t)-1;
> - /* Write to debug console. stderr is near enough. */
> - if (use_gdb_syscalls()) {
> + {
> + char c;
> + if (!get_user_u8(c, args)) {
> + /* Write to debug console. stderr is near enough. */
> + if (use_gdb_syscalls()) {
> return arm_gdb_syscall(cpu, arm_semi_cb, "write,2,%x,1",
> args);
> - } else {
> + } else {
> #ifdef CONFIG_SOFTMMU
> - Chardev *chardev = semihosting_get_chardev();
> - if (chardev) {
> - return qemu_chr_write_all(chardev, (uint8_t *) &c, 1);
> - } else
> + Chardev *chardev = semihosting_get_chardev();
> + if (chardev) {
> + return qemu_chr_write_all(chardev, (uint8_t *) &c, 1);
> + }
> #endif
Looks like this patch is dependent on some other patchset?
> @@ -447,20 +474,23 @@ target_ulong do_arm_semihosting(CPUARMState *env)
> GET_ARG(3);
> if (use_gdb_syscalls()) {
> return arm_gdb_syscall(cpu, arm_semi_cb, "rename,%s,%s",
> - arg0, (int)arg1+1, arg2, (int)arg3+1);
> + arg0, (int)arg1 + 1, arg2, (int)arg3 + 1);
> } else {
> char *s2;
> s = lock_user_string(arg0);
> s2 = lock_user_string(arg2);
> - if (!s || !s2)
> - /* FIXME - should this error code be -TARGET_EFAULT ? */
> - ret = (uint32_t)-1;
> - else
> + if (s && s2) {
> ret = set_swi_errno(ts, rename(s, s2));
> - if (s2)
> + } else {
> + ret = -EIO;
I would stick with -1 personally. The spec says "host-specific error
code", but since there's not a lot the guest can do with the result
anyway we can just use -1 in our implementation. Also, EIO is an
odd choice for "you passed us non-readable memory", which is more
usually EFAULT.
More generally, can you keep changes in behaviour in a separate patch
from code reformatting, please ?
> @@ -472,7 +502,7 @@ target_ulong do_arm_semihosting(CPUARMState *env)
> GET_ARG(1);
> if (use_gdb_syscalls()) {
> return arm_gdb_syscall(cpu, arm_semi_cb, "system,%s",
> - arg0, (int)arg1+1);
> + arg0, (int)arg1 + 1);
...here you don't have the space after the cast. I prefer this way.
thanks
-- PMM