Add x86-specific support for handling the CFA expression found in GNU linker generated .eh_frame for PLT.
This enables unwinding through GNU linker generated PLT entries on i386 and x86-64, unless linker option --no-ld-generated-unwind-info is used. Signed-off-by: Jens Remus <[email protected]> --- arch/x86/include/asm/unwind_user_eh_frame.h | 68 ++++++++++++++++++++- kernel/unwind/eh_frame.c | 3 +- kernel/unwind/eh_frame.h | 14 +++++ 3 files changed, 83 insertions(+), 2 deletions(-) diff --git a/arch/x86/include/asm/unwind_user_eh_frame.h b/arch/x86/include/asm/unwind_user_eh_frame.h index fdccbda2fe4b..8268eb1a0ff5 100644 --- a/arch/x86/include/asm/unwind_user_eh_frame.h +++ b/arch/x86/include/asm/unwind_user_eh_frame.h @@ -2,6 +2,8 @@ #ifndef _ASM_X86_UNWIND_USER_EH_FRAME_H #define _ASM_X86_UNWIND_USER_EH_FRAME_H +#include <linux/unwind_user_eh_frame_types.h> + #ifdef CONFIG_X86_64 #define EH_FRAME_REG_SP 7 /* designated stack pointer register */ @@ -15,7 +17,71 @@ #define EH_FRAME_MIN_DATA_ALIGN -8 #define EH_FRAME_MAX_DATA_ALIGN -1 -#endif +#endif /* CONFIG_X86_64 */ + +static inline int memcmp_masked(const void *s1, const void *s2, + const void *mask, size_t n) +{ + const unsigned char *p1 = s1, *p2 = s2, *m = mask; + int res = 0; + + while (n--) + if ((res = (*p1++ ^ *p2++) & *m++)) + break; + + return res; +} + +static inline int eh_frame_do_def_cfa_expression(const char *expr, + int size, + unsigned long ip, + struct eh_frame_reg_state *reg_state) +{ + /* + * PLT CFA expression: + * + * DW_OP_breg<SP> + <SP_offset> // 4 (ESP) + 4 or 7 (RSP) + 8 + * DW_OP_breg<IP> + 0 // 8 (EIP) or 16 (RIP) + * DW_OP_lit15 + * DW_OP_and + * DW_OP_lit<N> + * DW_OP_ge + * DW_OP_lit<shift> // 2 or 3 + * DW_OP_shl + * DW_OP_plus + * + * CFA = (SP + offset) + (((IP & 0xf) >= N) << shift) + */ + static const char plt_expr[] = {0x00,0x00,0x00,0x00,0x3f,0x1a,0x30,0x2a,0x30,0x24,0x22}; + static const char plt_mask[] = {0x00,0xf0,0x00,0xff,0xff,0xff,0xf0,0xff,0xf0,0xff,0xff}; + + if (size == sizeof(plt_expr) && + !memcmp_masked(expr, plt_expr, plt_mask, sizeof(plt_expr))) { + unsigned char sp_op = expr[0]; + unsigned char sp_offset = expr[1] & 0x0f; + unsigned char ip_op = expr[2]; + unsigned char n = DW_OP_lit_value(expr[6]); + unsigned char shift = DW_OP_lit_value(expr[8]); + unsigned char sp_reg, ip_reg; + + if (!DW_OP_is_breg(sp_op) || !DW_OP_is_breg(ip_op)) + return -EOPNOTSUPP; + + sp_reg = DW_OP_breg_register(sp_op); + ip_reg = DW_OP_breg_register(ip_op); + if (sp_reg != EH_FRAME_REG_SP || ip_reg != EH_FRAME_REG_RA) + return -EOPNOTSUPP; + + /* CFA = (SP + SP_offset) + (((IP & 0xf) >= N) << shift) */ + reg_state->cfa_rule = CFA_REG_OFFSET; + reg_state->cfa_regnum = EH_FRAME_REG_SP; + reg_state->cfa_offset = sp_offset + (((ip & 15) >= n) << shift); + return 0; + } + + return -EOPNOTSUPP; +} +#define eh_frame_do_def_cfa_expression eh_frame_do_def_cfa_expression #include <asm-generic/unwind_user_eh_frame.h> diff --git a/kernel/unwind/eh_frame.c b/kernel/unwind/eh_frame.c index a98804dbe588..0a81ba1a0377 100644 --- a/kernel/unwind/eh_frame.c +++ b/kernel/unwind/eh_frame.c @@ -15,11 +15,12 @@ #include <linux/types.h> #include <linux/unwind_user_types.h> #include <linux/unwind_user_eh_frame_types.h> -#include <asm/unwind_user_eh_frame.h> #include "eh_frame.h" #include "eh_frame_debug.h" +#include <asm/unwind_user_eh_frame.h> + struct eh_frame_cfi_context { struct eh_frame_reg_state state; struct eh_frame_reg_state stack[EH_FRAME_MAX_STATE_STACK]; diff --git a/kernel/unwind/eh_frame.h b/kernel/unwind/eh_frame.h index a43560486283..2f87d1b32bbc 100644 --- a/kernel/unwind/eh_frame.h +++ b/kernel/unwind/eh_frame.h @@ -60,6 +60,20 @@ #define DW_EH_PE_format(encoding) ((encoding) & 0x0f) #define DW_EH_PE_application(encoding) ((encoding) & 0x70) +/* DWARF expression operations */ +#define DW_OP_lit0 0x30 +/* ... */ +#define DW_OP_lit31 0x4f +#define DW_OP_breg0 0x70 +/* ... */ +#define DW_OP_breg31 0x8f + +/* Helpers for DWARF expression operations */ +#define DW_OP_is_lit(op) ((op) >= DW_OP_lit0 && (op) <= DW_OP_lit31) +#define DW_OP_is_breg(op) ((op) >= DW_OP_breg0 && (op) <= DW_OP_breg31) +#define DW_OP_lit_value(op) ((op) - DW_OP_lit0) +#define DW_OP_breg_register(op) ((op) - DW_OP_breg0) + /* CIE/FDE constants */ #define EH_FRAME_CIE_ID 0 #define EH_FRAME_DWARF64_LENGTH 0xffffffff -- 2.53.0
