Message ID | 20200108161535.6141-2-hjl.tools@gmail.com |
---|---|
State | New |
Headers | show |
Series | V2 [PATCH 1/5] i386: Don't unnecessarily save and restore EAX, ECX and EDX [BZ# 25262] | expand |
On 08/01/2020 13:15, H.J. Lu wrote: > On i386, since EAX, ECX and EDX are caller-saved, there are no need > to save and restore EAX, ECX and EDX in getcontext, setcontext and > swapcontext. They just need to clear EAX on success. The extra > scratch registers are needed to enable CET. > > Tested on i386. LGTM thanks. You might also remove the oE{A,C,D}X definitions from Linux i386 ucontext_i.sym. As a side note, Hurd might do the same on its implementations. Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org> > --- > sysdeps/unix/sysv/linux/i386/getcontext.S | 8 +------- > sysdeps/unix/sysv/linux/i386/setcontext.S | 11 ++++------- > sysdeps/unix/sysv/linux/i386/swapcontext.S | 17 +++++------------ > 3 files changed, 10 insertions(+), 26 deletions(-) > > diff --git a/sysdeps/unix/sysv/linux/i386/getcontext.S b/sysdeps/unix/sysv/linux/i386/getcontext.S > index f86df4d555..9c1df9a2aa 100644 > --- a/sysdeps/unix/sysv/linux/i386/getcontext.S > +++ b/sysdeps/unix/sysv/linux/i386/getcontext.S > @@ -26,13 +26,7 @@ ENTRY(__getcontext) > /* Load address of the context data structure. */ > movl 4(%esp), %eax > > - /* Return value of getcontext. EAX is the only register whose > - value is not preserved. */ > - movl $0, oEAX(%eax) > - > - /* Save the 32-bit register values and the return address. */ > - movl %ecx, oECX(%eax) > - movl %edx, oEDX(%eax) > + /* Save the preserved register values and the return address. */ > movl %edi, oEDI(%eax) > movl %esi, oESI(%eax) > movl %ebp, oEBP(%eax) Ok. > diff --git a/sysdeps/unix/sysv/linux/i386/setcontext.S b/sysdeps/unix/sysv/linux/i386/setcontext.S > index b4b5c0298c..f042d80bf4 100644 > --- a/sysdeps/unix/sysv/linux/i386/setcontext.S > +++ b/sysdeps/unix/sysv/linux/i386/setcontext.S > @@ -65,22 +65,19 @@ ENTRY(__setcontext) > cfi_offset (esi, oESI) > cfi_offset (ebp, oEBP) > cfi_offset (ebx, oEBX) > - cfi_offset (edx, oEDX) > - cfi_offset (ecx, oECX) > movl oESP(%eax), %esp > > /* Push the return address on the new stack so we can return there. */ > pushl %ecx > > - /* Load the values of all the 32-bit registers (except ESP). > - Since we are loading from EAX, it must be last. */ > + /* Load the values of all the preserved registers (except ESP). */ > movl oEDI(%eax), %edi > movl oESI(%eax), %esi > movl oEBP(%eax), %ebp > movl oEBX(%eax), %ebx > - movl oEDX(%eax), %edx > - movl oECX(%eax), %ecx > - movl oEAX(%eax), %eax > + > + /* All done, return 0 for success. */ > + xorl %eax, %eax > > /* End FDE here, we fall into another context. */ > cfi_endproc Ok. > diff --git a/sysdeps/unix/sysv/linux/i386/swapcontext.S b/sysdeps/unix/sysv/linux/i386/swapcontext.S > index 792bfdf7e6..090c2d8c3e 100644 > --- a/sysdeps/unix/sysv/linux/i386/swapcontext.S > +++ b/sysdeps/unix/sysv/linux/i386/swapcontext.S > @@ -26,13 +26,7 @@ ENTRY(__swapcontext) > /* Load address of the context data structure we save in. */ > movl 4(%esp), %eax > > - /* Return value of swapcontext. EAX is the only register whose > - value is not preserved. */ > - movl $0, oEAX(%eax) > - > - /* Save the 32-bit register values and the return address. */ > - movl %ecx, oECX(%eax) > - movl %edx, oEDX(%eax) > + /* Save the preserved register values and the return address. */ > movl %edi, oEDI(%eax) > movl %esi, oESI(%eax) > movl %ebp, oEBP(%eax) > @@ -91,15 +85,14 @@ ENTRY(__swapcontext) > /* Push the return address on the new stack so we can return there. */ > pushl %ecx > > - /* Load the values of all the 32-bit registers (except ESP). > - Since we are loading from EAX, it must be last. */ > + /* Load the values of all the preserved registers (except ESP). */ > movl oEDI(%eax), %edi > movl oESI(%eax), %esi > movl oEBP(%eax), %ebp > movl oEBX(%eax), %ebx > - movl oEDX(%eax), %edx > - movl oECX(%eax), %ecx > - movl oEAX(%eax), %eax > + > + /* All done, return 0 for success. */ > + xorl %eax, %eax > > /* The following 'ret' will pop the address of the code and jump > to it. */ >
diff --git a/sysdeps/unix/sysv/linux/i386/getcontext.S b/sysdeps/unix/sysv/linux/i386/getcontext.S index f86df4d555..9c1df9a2aa 100644 --- a/sysdeps/unix/sysv/linux/i386/getcontext.S +++ b/sysdeps/unix/sysv/linux/i386/getcontext.S @@ -26,13 +26,7 @@ ENTRY(__getcontext) /* Load address of the context data structure. */ movl 4(%esp), %eax - /* Return value of getcontext. EAX is the only register whose - value is not preserved. */ - movl $0, oEAX(%eax) - - /* Save the 32-bit register values and the return address. */ - movl %ecx, oECX(%eax) - movl %edx, oEDX(%eax) + /* Save the preserved register values and the return address. */ movl %edi, oEDI(%eax) movl %esi, oESI(%eax) movl %ebp, oEBP(%eax) diff --git a/sysdeps/unix/sysv/linux/i386/setcontext.S b/sysdeps/unix/sysv/linux/i386/setcontext.S index b4b5c0298c..f042d80bf4 100644 --- a/sysdeps/unix/sysv/linux/i386/setcontext.S +++ b/sysdeps/unix/sysv/linux/i386/setcontext.S @@ -65,22 +65,19 @@ ENTRY(__setcontext) cfi_offset (esi, oESI) cfi_offset (ebp, oEBP) cfi_offset (ebx, oEBX) - cfi_offset (edx, oEDX) - cfi_offset (ecx, oECX) movl oESP(%eax), %esp /* Push the return address on the new stack so we can return there. */ pushl %ecx - /* Load the values of all the 32-bit registers (except ESP). - Since we are loading from EAX, it must be last. */ + /* Load the values of all the preserved registers (except ESP). */ movl oEDI(%eax), %edi movl oESI(%eax), %esi movl oEBP(%eax), %ebp movl oEBX(%eax), %ebx - movl oEDX(%eax), %edx - movl oECX(%eax), %ecx - movl oEAX(%eax), %eax + + /* All done, return 0 for success. */ + xorl %eax, %eax /* End FDE here, we fall into another context. */ cfi_endproc diff --git a/sysdeps/unix/sysv/linux/i386/swapcontext.S b/sysdeps/unix/sysv/linux/i386/swapcontext.S index 792bfdf7e6..090c2d8c3e 100644 --- a/sysdeps/unix/sysv/linux/i386/swapcontext.S +++ b/sysdeps/unix/sysv/linux/i386/swapcontext.S @@ -26,13 +26,7 @@ ENTRY(__swapcontext) /* Load address of the context data structure we save in. */ movl 4(%esp), %eax - /* Return value of swapcontext. EAX is the only register whose - value is not preserved. */ - movl $0, oEAX(%eax) - - /* Save the 32-bit register values and the return address. */ - movl %ecx, oECX(%eax) - movl %edx, oEDX(%eax) + /* Save the preserved register values and the return address. */ movl %edi, oEDI(%eax) movl %esi, oESI(%eax) movl %ebp, oEBP(%eax) @@ -91,15 +85,14 @@ ENTRY(__swapcontext) /* Push the return address on the new stack so we can return there. */ pushl %ecx - /* Load the values of all the 32-bit registers (except ESP). - Since we are loading from EAX, it must be last. */ + /* Load the values of all the preserved registers (except ESP). */ movl oEDI(%eax), %edi movl oESI(%eax), %esi movl oEBP(%eax), %ebp movl oEBX(%eax), %ebx - movl oEDX(%eax), %edx - movl oECX(%eax), %ecx - movl oEAX(%eax), %eax + + /* All done, return 0 for success. */ + xorl %eax, %eax /* The following 'ret' will pop the address of the code and jump to it. */