Commit 88496161 authored by H. Peter Anvin's avatar H. Peter Anvin Committed by Dave Hansen
Browse files

x86/entry/vdso32: Remove open-coded DWARF in sigreturn.S 



The vdso32 sigreturn.S contains open-coded DWARF bytecode, which
includes a hack for gdb to not try to step back to a previous call
instruction when backtracing from a signal handler.

Neither of those are necessary anymore: the backtracing issue is
handled by ".cfi_entry simple" and ".cfi_signal_frame", both of which
have been supported for a very long time now, which allows the
remaining frame to be built using regular .cfi annotations.

Add a few more register offsets to the signal frame just for good
measure.

Replace the nop on fallthrough of the system call (which should never,
ever happen) with a ud2a trap.

Signed-off-by: default avatarH. Peter Anvin (Intel) <hpa@zytor.com>
Signed-off-by: default avatarDave Hansen <dave.hansen@linux.intel.com>
Link: https://patch.msgid.link/20251216212606.1325678-7-hpa@zytor.com
parent 98d3e996

arch/x86/entry/vdso/vdso32/sigreturn.S

+32 −114
Original line number Diff line number Diff line 
/* SPDX-License-Identifier: GPL-2.0 */

#include <linux/linkage.h>

#include <asm/unistd_32.h>

#include <asm/dwarf2.h>

#include <asm/asm-offsets.h>



.macro STARTPROC_SIGNAL_FRAME sc

	CFI_STARTPROC	simple

	CFI_SIGNAL_FRAME

	/* -4 as pretcode has already been popped */

	CFI_DEF_CFA	esp,	\sc - 4

	CFI_OFFSET	eip,    IA32_SIGCONTEXT_ip

	CFI_OFFSET	eax,    IA32_SIGCONTEXT_ax

	CFI_OFFSET	ebx,    IA32_SIGCONTEXT_bx

	CFI_OFFSET	ecx,    IA32_SIGCONTEXT_cx

	CFI_OFFSET	edx,    IA32_SIGCONTEXT_dx

	CFI_OFFSET	esp,    IA32_SIGCONTEXT_sp

	CFI_OFFSET	ebp,    IA32_SIGCONTEXT_bp

	CFI_OFFSET	esi,    IA32_SIGCONTEXT_si

	CFI_OFFSET	edi,    IA32_SIGCONTEXT_di

	CFI_OFFSET	es,     IA32_SIGCONTEXT_es

	CFI_OFFSET	cs,     IA32_SIGCONTEXT_cs

	CFI_OFFSET	ss,     IA32_SIGCONTEXT_ss

	CFI_OFFSET	ds,     IA32_SIGCONTEXT_ds

	CFI_OFFSET	eflags, IA32_SIGCONTEXT_flags

.endm



	.text

	.globl __kernel_sigreturn

	.type __kernel_sigreturn,@function

	nop /* this guy is needed for .LSTARTFDEDLSI1 below (watch for HACK) */

	ALIGN

__kernel_sigreturn:

.LSTART_sigreturn:

	popl %eax		/* XXX does this mean it needs unwind info? */

	STARTPROC_SIGNAL_FRAME IA32_SIGFRAME_sigcontext

	popl %eax

	CFI_ADJUST_CFA_OFFSET -4

	movl $__NR_sigreturn, %eax

	int $0x80

.LEND_sigreturn:

SYM_INNER_LABEL(vdso32_sigreturn_landing_pad, SYM_L_GLOBAL)

	nop

	.size __kernel_sigreturn,.-.LSTART_sigreturn

	ud2a

	CFI_ENDPROC

	.size __kernel_sigreturn,.-__kernel_sigreturn



	.globl __kernel_rt_sigreturn

	.type __kernel_rt_sigreturn,@function

	ALIGN

__kernel_rt_sigreturn:

.LSTART_rt_sigreturn:

	STARTPROC_SIGNAL_FRAME IA32_RT_SIGFRAME_sigcontext

	movl $__NR_rt_sigreturn, %eax

	int $0x80

.LEND_rt_sigreturn:

SYM_INNER_LABEL(vdso32_rt_sigreturn_landing_pad, SYM_L_GLOBAL)

	nop

	.size __kernel_rt_sigreturn,.-.LSTART_rt_sigreturn

	.previous



	.section .eh_frame,"a",@progbits

.LSTARTFRAMEDLSI1:

	.long .LENDCIEDLSI1-.LSTARTCIEDLSI1

.LSTARTCIEDLSI1:

	.long 0			/* CIE ID */

	.byte 1			/* Version number */

	.string "zRS"		/* NUL-terminated augmentation string */

	.uleb128 1		/* Code alignment factor */

	.sleb128 -4		/* Data alignment factor */

	.byte 8			/* Return address register column */

	.uleb128 1		/* Augmentation value length */

	.byte 0x1b		/* DW_EH_PE_pcrel|DW_EH_PE_sdata4. */

	.byte 0			/* DW_CFA_nop */

	.align 4

.LENDCIEDLSI1:

	.long .LENDFDEDLSI1-.LSTARTFDEDLSI1 /* Length FDE */

.LSTARTFDEDLSI1:

	.long .LSTARTFDEDLSI1-.LSTARTFRAMEDLSI1 /* CIE pointer */

	/* HACK: The dwarf2 unwind routines will subtract 1 from the

	   return address to get an address in the middle of the

	   presumed call instruction.  Since we didn't get here via

	   a call, we need to include the nop before the real start

	   to make up for it.  */

	.long .LSTART_sigreturn-1-.	/* PC-relative start address */

	.long .LEND_sigreturn-.LSTART_sigreturn+1

	.uleb128 0			/* Augmentation */

	/* What follows are the instructions for the table generation.

	   We record the locations of each register saved.  This is

	   complicated by the fact that the "CFA" is always assumed to

	   be the value of the stack pointer in the caller.  This means

	   that we must define the CFA of this body of code to be the

	   saved value of the stack pointer in the sigcontext.  Which

	   also means that there is no fixed relation to the other

	   saved registers, which means that we must use DW_CFA_expression

	   to compute their addresses.  It also means that when we

	   adjust the stack with the popl, we have to do it all over again.  */



#define do_cfa_expr(offset)						\

	.byte 0x0f;			/* DW_CFA_def_cfa_expression */	\

	.uleb128 1f-0f;			/*   length */			\

0:	.byte 0x74;			/*     DW_OP_breg4 */		\

	.sleb128 offset;		/*      offset */		\

	.byte 0x06;			/*     DW_OP_deref */		\

1:



#define do_expr(regno, offset)						\

	.byte 0x10;			/* DW_CFA_expression */		\

	.uleb128 regno;			/*   regno */			\

	.uleb128 1f-0f;			/*   length */			\

0:	.byte 0x74;			/*     DW_OP_breg4 */		\

	.sleb128 offset;		/*       offset */		\

1:



	do_cfa_expr(IA32_SIGCONTEXT_sp+4)

	do_expr(0, IA32_SIGCONTEXT_ax+4)

	do_expr(1, IA32_SIGCONTEXT_cx+4)

	do_expr(2, IA32_SIGCONTEXT_dx+4)

	do_expr(3, IA32_SIGCONTEXT_bx+4)

	do_expr(5, IA32_SIGCONTEXT_bp+4)

	do_expr(6, IA32_SIGCONTEXT_si+4)

	do_expr(7, IA32_SIGCONTEXT_di+4)

	do_expr(8, IA32_SIGCONTEXT_ip+4)



	.byte 0x42	/* DW_CFA_advance_loc 2 -- nop; popl eax. */



	do_cfa_expr(IA32_SIGCONTEXT_sp)

	do_expr(0, IA32_SIGCONTEXT_ax)

	do_expr(1, IA32_SIGCONTEXT_cx)

	do_expr(2, IA32_SIGCONTEXT_dx)

	do_expr(3, IA32_SIGCONTEXT_bx)

	do_expr(5, IA32_SIGCONTEXT_bp)

	do_expr(6, IA32_SIGCONTEXT_si)

	do_expr(7, IA32_SIGCONTEXT_di)

	do_expr(8, IA32_SIGCONTEXT_ip)



	.align 4

.LENDFDEDLSI1:



	.long .LENDFDEDLSI2-.LSTARTFDEDLSI2 /* Length FDE */

.LSTARTFDEDLSI2:

	.long .LSTARTFDEDLSI2-.LSTARTFRAMEDLSI1 /* CIE pointer */

	/* HACK: See above wrt unwind library assumptions.  */

	.long .LSTART_rt_sigreturn-1-.	/* PC-relative start address */

	.long .LEND_rt_sigreturn-.LSTART_rt_sigreturn+1

	.uleb128 0			/* Augmentation */

	/* What follows are the instructions for the table generation.

	   We record the locations of each register saved.  This is

	   slightly less complicated than the above, since we don't

	   modify the stack pointer in the process.  */



	do_cfa_expr(IA32_RT_SIGFRAME_sigcontext-4 + IA32_SIGCONTEXT_sp)

	do_expr(0, IA32_RT_SIGFRAME_sigcontext-4 + IA32_SIGCONTEXT_ax)

	do_expr(1, IA32_RT_SIGFRAME_sigcontext-4 + IA32_SIGCONTEXT_cx)

	do_expr(2, IA32_RT_SIGFRAME_sigcontext-4 + IA32_SIGCONTEXT_dx)

	do_expr(3, IA32_RT_SIGFRAME_sigcontext-4 + IA32_SIGCONTEXT_bx)

	do_expr(5, IA32_RT_SIGFRAME_sigcontext-4 + IA32_SIGCONTEXT_bp)

	do_expr(6, IA32_RT_SIGFRAME_sigcontext-4 + IA32_SIGCONTEXT_si)

	do_expr(7, IA32_RT_SIGFRAME_sigcontext-4 + IA32_SIGCONTEXT_di)

	do_expr(8, IA32_RT_SIGFRAME_sigcontext-4 + IA32_SIGCONTEXT_ip)



	.align 4

.LENDFDEDLSI2:

	ud2a

	CFI_ENDPROC

	.size __kernel_rt_sigreturn,.-__kernel_rt_sigreturn

	.previous

arch/x86/include/asm/dwarf2.h

+1 −0
Original line number Diff line number Diff line
@@ -20,6 +20,7 @@ 
#define CFI_RESTORE_STATE	.cfi_restore_state

#define CFI_UNDEFINED		.cfi_undefined

#define CFI_ESCAPE		.cfi_escape

#define CFI_SIGNAL_FRAME	.cfi_signal_frame



#ifndef BUILD_VDSO

	/*

arch/x86/kernel/asm-offsets.c

+6 −0
Original line number Diff line number Diff line
@@ -63,8 +63,14 @@ static void __used common(void) 
	OFFSET(IA32_SIGCONTEXT_bp, sigcontext_32, bp);

	OFFSET(IA32_SIGCONTEXT_sp, sigcontext_32, sp);

	OFFSET(IA32_SIGCONTEXT_ip, sigcontext_32, ip);

	OFFSET(IA32_SIGCONTEXT_es, sigcontext_32, es);

	OFFSET(IA32_SIGCONTEXT_cs, sigcontext_32, cs);

	OFFSET(IA32_SIGCONTEXT_ss, sigcontext_32, ss);

	OFFSET(IA32_SIGCONTEXT_ds, sigcontext_32, ds);

	OFFSET(IA32_SIGCONTEXT_flags, sigcontext_32, flags);



	BLANK();

	OFFSET(IA32_SIGFRAME_sigcontext,    sigframe_ia32,    sc);

	OFFSET(IA32_RT_SIGFRAME_sigcontext, rt_sigframe_ia32, uc.uc_mcontext);

#endif