[PATCH 1/1] Only pass the minimum number of syscall arguments
Kito Cheng
kito.cheng@gmail.com
Tue Feb 11 06:55:00 GMT 2020
Hi Georg:
LGTM, great job, it reduce the code size for libgloss.
Tested rv32gc/rv64gc on qemu.
Thanks :)
On Tue, Feb 11, 2020 at 4:20 AM Georg Sauthoff <mail@gms.tf> wrote:
>
> Previously, __internal_syscall() compiled into asm-code that unconditionally
> sets the syscall argument registers a0 to a5.
>
> For example, the instruction sequence for a exit syscall looked like
> this:
>
> li a0, 1 # in ther caller of exit()
> # ... # in newlib:
> li a1, 0 # unused arguments
> li a2, 0
> li a3, 0
> li a4, 0
> li a5, 0
> li a7, 93 # exit syscall number
>
> (i.e. the binary contains then 5 superfluous instructions for this
> one argument syscall)
>
> This commit changes the RISC-V syscall code such that only the required
> syscall argument registers are set.
>
> GCC detects that argc is known at compile time and thus evaluates all the
> if-statements where argc is used at compile time (tested with -O2 and -Os).
> ---
> libgloss/riscv/internal_syscall.h | 41 ++++++++++++++++++++++---------
> libgloss/riscv/sys_access.c | 2 +-
> libgloss/riscv/sys_close.c | 2 +-
> libgloss/riscv/sys_exit.c | 2 +-
> libgloss/riscv/sys_faccessat.c | 2 +-
> libgloss/riscv/sys_fstat.c | 2 +-
> libgloss/riscv/sys_fstatat.c | 2 +-
> libgloss/riscv/sys_gettimeofday.c | 2 +-
> libgloss/riscv/sys_link.c | 2 +-
> libgloss/riscv/sys_lseek.c | 2 +-
> libgloss/riscv/sys_lstat.c | 2 +-
> libgloss/riscv/sys_open.c | 2 +-
> libgloss/riscv/sys_openat.c | 2 +-
> libgloss/riscv/sys_read.c | 2 +-
> libgloss/riscv/sys_sbrk.c | 4 +--
> libgloss/riscv/sys_stat.c | 2 +-
> libgloss/riscv/sys_unlink.c | 2 +-
> libgloss/riscv/sys_write.c | 2 +-
> 18 files changed, 48 insertions(+), 29 deletions(-)
>
> diff --git a/libgloss/riscv/internal_syscall.h b/libgloss/riscv/internal_syscall.h
> index e5d5594..1f1f42f 100644
> --- a/libgloss/riscv/internal_syscall.h
> +++ b/libgloss/riscv/internal_syscall.h
> @@ -22,31 +22,50 @@ __syscall_error(long a0)
> }
>
> static inline long
> -__internal_syscall(long n, long _a0, long _a1, long _a2, long _a3, long _a4, long _a5)
> +__internal_syscall(long n, int argc, long _a0, long _a1, long _a2, long _a3, long _a4, long _a5)
> {
> +#ifdef __riscv_32e
> + register long syscall_id asm("t0") = n;
> +#else
> + register long syscall_id asm("a7") = n;
> +#endif
> +
> register long a0 asm("a0") = _a0;
> + if (argc < 2) {
> + asm volatile ("ecall" : "+r"(a0) : "r"(syscall_id));
> + return a0;
> + }
> register long a1 asm("a1") = _a1;
> + if (argc == 2) {
> + asm volatile ("ecall" : "+r"(a0) : "r"(a1), "r"(syscall_id));
> + return a0;
> + }
> register long a2 asm("a2") = _a2;
> + if (argc == 3) {
> + asm volatile ("ecall" : "+r"(a0) : "r"(a1), "r"(a2), "r"(syscall_id));
> + return a0;
> + }
> register long a3 asm("a3") = _a3;
> + if (argc == 4) {
> + asm volatile ("ecall" : "+r"(a0) : "r"(a1), "r"(a2), "r"(a3), "r"(syscall_id));
> + return a0;
> + }
> register long a4 asm("a4") = _a4;
> + if (argc == 5) {
> + asm volatile ("ecall" : "+r"(a0) : "r"(a1), "r"(a2), "r"(a3), "r"(a4), "r"(syscall_id));
> + return a0;
> + }
> register long a5 asm("a5") = _a5;
>
> -#ifdef __riscv_32e
> - register long syscall_id asm("t0") = n;
> -#else
> - register long syscall_id asm("a7") = n;
> -#endif
> -
> - asm volatile ("scall"
> - : "+r"(a0) : "r"(a1), "r"(a2), "r"(a3), "r"(a4), "r"(a5), "r"(syscall_id));
> + asm volatile ("ecall" : "+r"(a0) : "r"(a1), "r"(a2), "r"(a3), "r"(a4), "r"(a5), "r"(syscall_id));
>
> return a0;
> }
>
> static inline long
> -syscall_errno(long n, long _a0, long _a1, long _a2, long _a3, long _a4, long _a5)
> +syscall_errno(long n, int argc, long _a0, long _a1, long _a2, long _a3, long _a4, long _a5)
> {
> - long a0 = __internal_syscall (n, _a0, _a1, _a2, _a3, _a4, _a5);
> + long a0 = __internal_syscall (n, argc, _a0, _a1, _a2, _a3, _a4, _a5);
>
> if (a0 < 0)
> return __syscall_error (a0);
> diff --git a/libgloss/riscv/sys_access.c b/libgloss/riscv/sys_access.c
> index ef446d2..45bedb3 100644
> --- a/libgloss/riscv/sys_access.c
> +++ b/libgloss/riscv/sys_access.c
> @@ -5,5 +5,5 @@
> int
> _access(const char *file, int mode)
> {
> - return syscall_errno (SYS_access, file, mode, 0, 0, 0, 0);
> + return syscall_errno (SYS_access, 2, file, mode, 0, 0, 0, 0);
> }
> diff --git a/libgloss/riscv/sys_close.c b/libgloss/riscv/sys_close.c
> index 80b10c6..c1691d8 100644
> --- a/libgloss/riscv/sys_close.c
> +++ b/libgloss/riscv/sys_close.c
> @@ -5,5 +5,5 @@
> int
> _close(int file)
> {
> - return syscall_errno (SYS_close, file, 0, 0, 0, 0, 0);
> + return syscall_errno (SYS_close, 1, file, 0, 0, 0, 0, 0);
> }
> diff --git a/libgloss/riscv/sys_exit.c b/libgloss/riscv/sys_exit.c
> index 03e1c34..995dd65 100644
> --- a/libgloss/riscv/sys_exit.c
> +++ b/libgloss/riscv/sys_exit.c
> @@ -5,6 +5,6 @@
> void
> _exit(int exit_status)
> {
> - syscall_errno (SYS_exit, exit_status, 0, 0, 0, 0, 0);
> + syscall_errno (SYS_exit, 1, exit_status, 0, 0, 0, 0, 0);
> while (1);
> }
> diff --git a/libgloss/riscv/sys_faccessat.c b/libgloss/riscv/sys_faccessat.c
> index e966a4a..6418ef4 100644
> --- a/libgloss/riscv/sys_faccessat.c
> +++ b/libgloss/riscv/sys_faccessat.c
> @@ -4,5 +4,5 @@
> /* Permissions of a file (by name) in a given directory. */
> int _faccessat(int dirfd, const char *file, int mode, int flags)
> {
> - return syscall_errno (SYS_faccessat, dirfd, file, mode, flags, 0, 0);
> + return syscall_errno (SYS_faccessat, 4, dirfd, file, mode, flags, 0, 0);
> }
> diff --git a/libgloss/riscv/sys_fstat.c b/libgloss/riscv/sys_fstat.c
> index 13a0bca..d97ba44 100644
> --- a/libgloss/riscv/sys_fstat.c
> +++ b/libgloss/riscv/sys_fstat.c
> @@ -9,7 +9,7 @@ int
> _fstat(int file, struct stat *st)
> {
> struct kernel_stat kst;
> - int rv = syscall_errno (SYS_fstat, file, &kst, 0, 0, 0, 0);
> + int rv = syscall_errno (SYS_fstat, 2, file, &kst, 0, 0, 0, 0);
> _conv_stat (st, &kst);
> return rv;
> }
> diff --git a/libgloss/riscv/sys_fstatat.c b/libgloss/riscv/sys_fstatat.c
> index 0e4ea42..bf03355 100644
> --- a/libgloss/riscv/sys_fstatat.c
> +++ b/libgloss/riscv/sys_fstatat.c
> @@ -8,7 +8,7 @@ int
> _fstatat(int dirfd, const char *file, struct stat *st, int flags)
> {
> struct kernel_stat kst;
> - int rv = syscall_errno (SYS_fstatat, dirfd, file, &kst, flags, 0, 0);
> + int rv = syscall_errno (SYS_fstatat, 4, dirfd, file, &kst, flags, 0, 0);
> _conv_stat (st, &kst);
> return rv;
> }
> diff --git a/libgloss/riscv/sys_gettimeofday.c b/libgloss/riscv/sys_gettimeofday.c
> index 457dcbc..daa14e4 100644
> --- a/libgloss/riscv/sys_gettimeofday.c
> +++ b/libgloss/riscv/sys_gettimeofday.c
> @@ -6,5 +6,5 @@
> int
> _gettimeofday(struct timeval *tp, void *tzp)
> {
> - return syscall_errno (SYS_gettimeofday, tp, 0, 0, 0, 0, 0);
> + return syscall_errno (SYS_gettimeofday, 1, tp, 0, 0, 0, 0, 0);
> }
> diff --git a/libgloss/riscv/sys_link.c b/libgloss/riscv/sys_link.c
> index eaeb22b..83cd1b2 100644
> --- a/libgloss/riscv/sys_link.c
> +++ b/libgloss/riscv/sys_link.c
> @@ -4,5 +4,5 @@
> /* Establish a new name for an existing file. */
> int _link(const char *old_name, const char *new_name)
> {
> - return syscall_errno (SYS_link, old_name, new_name, 0, 0, 0, 0);
> + return syscall_errno (SYS_link, 2, old_name, new_name, 0, 0, 0, 0);
> }
> diff --git a/libgloss/riscv/sys_lseek.c b/libgloss/riscv/sys_lseek.c
> index 7486a3a..8eb8b81 100644
> --- a/libgloss/riscv/sys_lseek.c
> +++ b/libgloss/riscv/sys_lseek.c
> @@ -6,5 +6,5 @@
> off_t
> _lseek(int file, off_t ptr, int dir)
> {
> - return syscall_errno (SYS_lseek, file, ptr, dir, 0, 0, 0);
> + return syscall_errno (SYS_lseek, 3, file, ptr, dir, 0, 0, 0);
> }
> diff --git a/libgloss/riscv/sys_lstat.c b/libgloss/riscv/sys_lstat.c
> index 2eeabcc..dd5dc52 100644
> --- a/libgloss/riscv/sys_lstat.c
> +++ b/libgloss/riscv/sys_lstat.c
> @@ -7,7 +7,7 @@
> int _lstat(const char *file, struct stat *st)
> {
> struct kernel_stat kst;
> - int rv = syscall_errno (SYS_lstat, file, &kst, 0, 0, 0, 0);
> + int rv = syscall_errno (SYS_lstat, 2, file, &kst, 0, 0, 0, 0);
> _conv_stat (st, &kst);
> return rv;
> }
> diff --git a/libgloss/riscv/sys_open.c b/libgloss/riscv/sys_open.c
> index 4fd5d67..eb1a99b 100644
> --- a/libgloss/riscv/sys_open.c
> +++ b/libgloss/riscv/sys_open.c
> @@ -5,5 +5,5 @@
> int
> _open(const char *name, int flags, int mode)
> {
> - return syscall_errno (SYS_open, name, flags, mode, 0, 0, 0);
> + return syscall_errno (SYS_open, 3, name, flags, mode, 0, 0, 0);
> }
> diff --git a/libgloss/riscv/sys_openat.c b/libgloss/riscv/sys_openat.c
> index cf429b7..652ab2e 100644
> --- a/libgloss/riscv/sys_openat.c
> +++ b/libgloss/riscv/sys_openat.c
> @@ -4,5 +4,5 @@
> /* Open file relative to given directory. */
> int _openat(int dirfd, const char *name, int flags, int mode)
> {
> - return syscall_errno (SYS_openat, dirfd, name, flags, mode, 0, 0);
> + return syscall_errno (SYS_openat, 4, dirfd, name, flags, mode, 0, 0);
> }
> diff --git a/libgloss/riscv/sys_read.c b/libgloss/riscv/sys_read.c
> index 7367e26..dd3bc33 100644
> --- a/libgloss/riscv/sys_read.c
> +++ b/libgloss/riscv/sys_read.c
> @@ -5,5 +5,5 @@
> /* Read from a file. */
> ssize_t _read(int file, void *ptr, size_t len)
> {
> - return syscall_errno (SYS_read, file, ptr, len, 0, 0, 0);
> + return syscall_errno (SYS_read, 3, file, ptr, len, 0, 0, 0);
> }
> diff --git a/libgloss/riscv/sys_sbrk.c b/libgloss/riscv/sys_sbrk.c
> index f91c2c5..086509e 100644
> --- a/libgloss/riscv/sys_sbrk.c
> +++ b/libgloss/riscv/sys_sbrk.c
> @@ -41,13 +41,13 @@ _sbrk(ptrdiff_t incr)
>
> if (heap_end == 0)
> {
> - long brk = __internal_syscall (SYS_brk, 0, 0, 0, 0, 0, 0);
> + long brk = __internal_syscall (SYS_brk, 1, 0, 0, 0, 0, 0, 0);
> if (brk == -1)
> return (void *)__syscall_error (-ENOMEM);
> heap_end = brk;
> }
>
> - if (__internal_syscall (SYS_brk, heap_end + incr, 0, 0, 0, 0, 0) != heap_end + incr)
> + if (__internal_syscall (SYS_brk, 1, heap_end + incr, 0, 0, 0, 0, 0) != heap_end + incr)
> return (void *)__syscall_error (-ENOMEM);
>
> heap_end += incr;
> diff --git a/libgloss/riscv/sys_stat.c b/libgloss/riscv/sys_stat.c
> index a193b10..1e03700 100644
> --- a/libgloss/riscv/sys_stat.c
> +++ b/libgloss/riscv/sys_stat.c
> @@ -8,7 +8,7 @@ int
> _stat(const char *file, struct stat *st)
> {
> struct kernel_stat kst;
> - int rv = syscall_errno (SYS_stat, file, &kst, 0, 0, 0, 0);
> + int rv = syscall_errno (SYS_stat, 2, file, &kst, 0, 0, 0, 0);
> _conv_stat (st, &kst);
> return rv;
> }
> diff --git a/libgloss/riscv/sys_unlink.c b/libgloss/riscv/sys_unlink.c
> index b55fe1e..1cf6bbe 100644
> --- a/libgloss/riscv/sys_unlink.c
> +++ b/libgloss/riscv/sys_unlink.c
> @@ -5,5 +5,5 @@
> int
> _unlink(const char *name)
> {
> - return syscall_errno (SYS_unlink, name, 0, 0, 0, 0, 0);
> + return syscall_errno (SYS_unlink, 1, name, 0, 0, 0, 0, 0);
> }
> diff --git a/libgloss/riscv/sys_write.c b/libgloss/riscv/sys_write.c
> index b972734..ce2edd3 100644
> --- a/libgloss/riscv/sys_write.c
> +++ b/libgloss/riscv/sys_write.c
> @@ -6,5 +6,5 @@
> ssize_t
> _write(int file, const void *ptr, size_t len)
> {
> - return syscall_errno (SYS_write, file, ptr, len, 0, 0, 0);
> + return syscall_errno (SYS_write, 3, file, ptr, len, 0, 0, 0);
> }
> --
> 2.24.1
>
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