Re: [PATCH v6 13/25] powerpc: Remove direct call to mmap2 syscall handlers
From: Michael Ellerman <mpe@ellerman.id.au>
Date: 2022-09-28 12:15:44
Rohan McLure [off-list ref] writes:
quoted hunk ↗ jump to hunk
Syscall handlers should not be invoked internally by their symbol names, as these symbols defined by the architecture-defined SYSCALL_DEFINE macro. Move the compatibility syscall definition for mmap2 to syscalls.c, so that all mmap implementations can share a helper function. Remove 'inline' on static mmap helper. Signed-off-by: Rohan McLure <redacted> Reviewed-by: Nicholas Piggin <npiggin@gmail.com> --- V2: Move mmap2 compat implementation to asm/kernel/syscalls.c. V4: Move to be applied before syscall wrapper introduced. V5: Remove 'inline' in helper. --- arch/powerpc/kernel/sys_ppc32.c | 9 --------- arch/powerpc/kernel/syscalls.c | 17 ++++++++++++++--- 2 files changed, 14 insertions(+), 12 deletions(-)diff --git a/arch/powerpc/kernel/sys_ppc32.c b/arch/powerpc/kernel/sys_ppc32.c index d961634976d8..776ae7565fc5 100644 --- a/arch/powerpc/kernel/sys_ppc32.c +++ b/arch/powerpc/kernel/sys_ppc32.c@@ -25,7 +25,6 @@ #include <linux/poll.h> #include <linux/personality.h> #include <linux/stat.h> -#include <linux/mman.h> #include <linux/in.h> #include <linux/syscalls.h> #include <linux/unistd.h>@@ -48,14 +47,6 @@ #include <asm/syscalls.h> #include <asm/switch_to.h> -unsigned long compat_sys_mmap2(unsigned long addr, size_t len, - unsigned long prot, unsigned long flags, - unsigned long fd, unsigned long pgoff) -{ - /* This should remain 12 even if PAGE_SIZE changes */ - return sys_mmap(addr, len, prot, flags, fd, pgoff << 12); -} - compat_ssize_t compat_sys_pread64(unsigned int fd, char __user *ubuf, compat_size_t count, u32 reg6, u32 pos1, u32 pos2) {diff --git a/arch/powerpc/kernel/syscalls.c b/arch/powerpc/kernel/syscalls.c index a04c97faa21a..9830957498b0 100644 --- a/arch/powerpc/kernel/syscalls.c +++ b/arch/powerpc/kernel/syscalls.c@@ -36,9 +36,9 @@ #include <asm/time.h> #include <asm/unistd.h> -static inline long do_mmap2(unsigned long addr, size_t len, - unsigned long prot, unsigned long flags, - unsigned long fd, unsigned long off, int shift) +static long do_mmap2(unsigned long addr, size_t len, + unsigned long prot, unsigned long flags, + unsigned long fd, unsigned long off, int shift) { if (!arch_validate_prot(prot, addr)) return -EINVAL;@@ -56,6 +56,17 @@ SYSCALL_DEFINE6(mmap2, unsigned long, addr, size_t, len, return do_mmap2(addr, len, prot, flags, fd, pgoff, PAGE_SHIFT-12); } +#ifdef CONFIG_COMPAT +COMPAT_SYSCALL_DEFINE6(mmap2, + unsigned long, addr, size_t, len, + unsigned long, prot, unsigned long, flags, + unsigned long, fd, unsigned long, pgoff) +{ + /* This should remain 12 even if PAGE_SIZE changes */ + return do_mmap2(addr, len, prot, flags, fd, pgoff << 12, PAGE_SHIFT-12);
This isn't quite right.
The comment about it remaining 12 is kind of misleading, it was true
when compat_sys_mmap2() called sys_mmap(), but it's wrong now that we're
calling do_mmap2().
The incoming "pgoff" here is in units of 4K.
do_mmap2() takes "off" in whatever units, but also takes "shift", which
has to tell us how to shift "off" into PAGE_SIZE units.
If we pass off = pgoff << 12, that's in bytes, so we need to page
shift = PAGE_SHIFT.
But I think it makes more sense to do the same as mmap2() and pass the
4K offset through, and pass shift = PAGE_SHIFT - 12. I also borrowed the
"off_4k" name from arm64. End result:
#ifdef CONFIG_COMPAT
COMPAT_SYSCALL_DEFINE6(mmap2,
unsigned long, addr, size_t, len,
unsigned long, prot, unsigned long, flags,
unsigned long, fd, unsigned long, off_4k)
{
return do_mmap2(addr, len, prot, flags, fd, off_4k, PAGE_SHIFT-12);
}
#endif
With that my G5 boots again :)
cheers