Date: Sat, 25 Aug 2012 00:16:55 +0200 From: Jilles Tjoelker <jilles@stack.nl> To: freebsd-hackers@freebsd.org Subject: [patch] libc: Do not export .cerror Message-ID: <20120824221655.GA76607@stack.nl>
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For some reason, libc exports the symbol .cerror (HIDENAME(cerror)), albeit in the FBSDprivate_1.0 version. It looks like there is no reason for this since it is not used from other libraries. Given that it cannot be accessed from C and its strange calling convention, it is rather unlikely that other things rely on it. Perhaps it is from a time when symbols could not be hidden. Not exporting .cerror causes it to be jumped to directly instead of via the PLT. The below patch is for i386 only and also takes advantage of .cerror's new status by not saving and loading %ebx before jumping to it. (Therefore, .cerror now saves and loads %ebx itself.) Where there was a conditional jump to a jump to .cerror, the conditional jump has been changed to jump to .cerror directly (many modern CPUs don't do static prediction and in any case it is not much of a benefit anyway). The patch decreases the size of libc.so.7 by a few kilobytes. Similar changes could be made to other architectures, and there may be more symbols that are exported but need not be. Index: lib/libc/i386/Symbol.map =================================================================== --- lib/libc/i386/Symbol.map (revision 239195) +++ lib/libc/i386/Symbol.map (working copy) @@ -63,7 +63,6 @@ __sys_vfork; _vfork; _end; - .cerror; _brk; .curbrk; .minbrk; Index: lib/libc/i386/SYS.h =================================================================== --- lib/libc/i386/SYS.h (revision 239195) +++ lib/libc/i386/SYS.h (working copy) @@ -36,21 +36,21 @@ #include <sys/syscall.h> #include <machine/asm.h> -#define SYSCALL(x) 2: PIC_PROLOGUE; jmp PIC_PLT(HIDENAME(cerror)); \ - ENTRY(__CONCAT(__sys_,x)); \ +#define SYSCALL(x) ENTRY(__CONCAT(__sys_,x)); \ .weak CNAME(x); \ .set CNAME(x),CNAME(__CONCAT(__sys_,x)); \ .weak CNAME(__CONCAT(_,x)); \ .set CNAME(__CONCAT(_,x)),CNAME(__CONCAT(__sys_,x)); \ - mov __CONCAT($SYS_,x),%eax; KERNCALL; jb 2b + mov __CONCAT($SYS_,x),%eax; KERNCALL; \ + jb HIDENAME(cerror) #define RSYSCALL(x) SYSCALL(x); ret; END(__CONCAT(__sys_,x)) -#define PSEUDO(x) 2: PIC_PROLOGUE; jmp PIC_PLT(HIDENAME(cerror)); \ - ENTRY(__CONCAT(__sys_,x)); \ +#define PSEUDO(x) ENTRY(__CONCAT(__sys_,x)); \ .weak CNAME(__CONCAT(_,x)); \ .set CNAME(__CONCAT(_,x)),CNAME(__CONCAT(__sys_,x)); \ - mov __CONCAT($SYS_,x),%eax; KERNCALL; jb 2b; ret; \ + mov __CONCAT($SYS_,x),%eax; KERNCALL; \ + jb HIDENAME(cerror); ret; \ END(__CONCAT(__sys_,x)) /* gas messes up offset -- although we don't currently need it, do for BCS */ Index: lib/libc/i386/gen/rfork_thread.S =================================================================== --- lib/libc/i386/gen/rfork_thread.S (revision 239195) +++ lib/libc/i386/gen/rfork_thread.S (working copy) @@ -113,8 +113,7 @@ popl %esi movl %ebp, %esp popl %ebp - PIC_PROLOGUE - jmp PIC_PLT(HIDENAME(cerror)) + jmp HIDENAME(cerror) END(rfork_thread) .section .note.GNU-stack,"",%progbits Index: lib/libc/i386/sys/brk.S =================================================================== --- lib/libc/i386/sys/brk.S (revision 239195) +++ lib/libc/i386/sys/brk.S (working copy) @@ -58,14 +58,11 @@ ok: mov $SYS_break,%eax KERNCALL - jb err + jb HIDENAME(cerror) movl 4(%esp),%eax movl %eax,(%edx) movl $0,%eax ret -err: - PIC_PROLOGUE - jmp PIC_PLT(HIDENAME(cerror)) #else @@ -77,13 +74,11 @@ ok: mov $SYS_break,%eax KERNCALL - jb err + jb HIDENAME(cerror) movl 4(%esp),%eax movl %eax,HIDENAME(curbrk) movl $0,%eax ret -err: - jmp HIDENAME(cerror) #endif END(brk) Index: lib/libc/i386/sys/getcontext.S =================================================================== --- lib/libc/i386/sys/getcontext.S (revision 239195) +++ lib/libc/i386/sys/getcontext.S (working copy) @@ -42,12 +42,9 @@ movl (%esp),%ecx /* save getcontext return address */ mov $SYS_getcontext,%eax KERNCALL - jb 1f + jb HIDENAME(cerror) addl $4,%esp /* remove stale (setcontext) return address */ jmp *%ecx /* restore return address */ -1: - PIC_PROLOGUE - jmp PIC_PLT(HIDENAME(cerror)) END(__sys_getcontext) .section .note.GNU-stack,"",%progbits Index: lib/libc/i386/sys/cerror.S =================================================================== --- lib/libc/i386/sys/cerror.S (revision 239195) +++ lib/libc/i386/sys/cerror.S (working copy) @@ -48,13 +48,14 @@ .globl CNAME(__error) .type CNAME(__error),@function HIDENAME(cerror): +#ifdef PIC + PIC_PROLOGUE pushl %eax -#ifdef PIC - /* The caller must execute the PIC prologue before jumping to cerror. */ call PIC_PLT(CNAME(__error)) popl %ecx PIC_EPILOGUE #else + pushl %eax call CNAME(__error) popl %ecx #endif Index: lib/libc/i386/sys/sbrk.S =================================================================== --- lib/libc/i386/sys/sbrk.S (revision 239195) +++ lib/libc/i386/sys/sbrk.S (working copy) @@ -59,7 +59,7 @@ addl %eax,4(%esp) mov $SYS_break,%eax KERNCALL - jb err + jb HIDENAME(cerror) PIC_PROLOGUE movl PIC_GOT(HIDENAME(curbrk)),%edx movl (%edx),%eax @@ -67,9 +67,6 @@ PIC_EPILOGUE back: ret -err: - PIC_PROLOGUE - jmp PIC_PLT(HIDENAME(cerror)) #else /* !PIC */ @@ -80,13 +77,11 @@ addl %eax,4(%esp) mov $SYS_break,%eax KERNCALL - jb err + jb HIDENAME(cerror) movl HIDENAME(curbrk),%eax addl %ecx,HIDENAME(curbrk) back: ret -err: - jmp HIDENAME(cerror) #endif /* PIC */ END(sbrk) Index: lib/libc/i386/sys/Ovfork.S =================================================================== --- lib/libc/i386/sys/Ovfork.S (revision 239195) +++ lib/libc/i386/sys/Ovfork.S (working copy) @@ -50,8 +50,7 @@ jmp *%ecx 1: pushl %ecx - PIC_PROLOGUE - jmp PIC_PLT(HIDENAME(cerror)) + jmp HIDENAME(cerror) END(__sys_vfork) .section .note.GNU-stack,"",%progbits Index: lib/libc/i386/sys/ptrace.S =================================================================== --- lib/libc/i386/sys/ptrace.S (revision 239195) +++ lib/libc/i386/sys/ptrace.S (working copy) @@ -50,11 +50,8 @@ #endif mov $SYS_ptrace,%eax KERNCALL - jb err + jb HIDENAME(cerror) ret -err: - PIC_PROLOGUE - jmp PIC_PLT(HIDENAME(cerror)) END(ptrace) .section .note.GNU-stack,"",%progbits Index: lib/libc/i386/sys/exect.S =================================================================== --- lib/libc/i386/sys/exect.S (revision 239195) +++ lib/libc/i386/sys/exect.S (working copy) @@ -47,8 +47,7 @@ pushl %edx popf KERNCALL - PIC_PROLOGUE - jmp PIC_PLT(HIDENAME(cerror)) /* exect(file, argv, env); */ + jmp HIDENAME(cerror) /* exect(file, argv, env); */ END(exect) .section .note.GNU-stack,"",%progbits Index: lib/libc/i386/sys/syscall.S =================================================================== --- lib/libc/i386/sys/syscall.S (revision 239195) +++ lib/libc/i386/sys/syscall.S (working copy) @@ -45,11 +45,8 @@ KERNCALL push %ecx /* need to push a word to keep stack frame intact upon return; the word must be the return address. */ - jb 1f + jb HIDENAME(cerror) ret -1: - PIC_PROLOGUE - jmp PIC_PLT(HIDENAME(cerror)) END(syscall) .section .note.GNU-stack,"",%progbits -- Jilles Tjoelker
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