arch/x86/exception-tables.rst

1 .. SPDX-License-Identifier: GPL-2.0
27 hardware present in every Linux-capable CPU handle this test.
51 (i.e. regs->eip) to find an address where the execution can continue
53 return address (again regs->eip) and returns. The execution will
73       long __gu_err = - 14 , __gu_val = 0;
75       if (((((0 + current_set[0])->tss.segment) == 0x18 )  ||
77         ((unsigned long)(__gu_addr ) <= 0xC0000000UL - (sizeof(*(buf)))))))
93                               (   __gu_addr   )) ), "i"(- 14 ), "0"(  __gu_err  )) ;
107                               (   __gu_addr   )) ), "i"(- 14 ), "0"(  __gu_err  ));
120                               (   __gu_addr   )) ), "i"(- 14 ), "0"(__gu_err));
138  >         cmpl $-1073741825,64(%esp)
147  > 3:      movl $-14,%eax
165  > objdump --section-headers vmlinux
167  > vmlinux:     file format elf32-i386
172  >                   CONTENTS, ALLOC, LOAD, READONLY, CODE
174  >                   CONTENTS, ALLOC, LOAD, READONLY, CODE
176  >                   CONTENTS, ALLOC, LOAD, READONLY, DATA
178  >                   CONTENTS, ALLOC, LOAD, READONLY, DATA
180  >                   CONTENTS, ALLOC, LOAD, DATA
192  > objdump --disassemble --section=.text vmlinux
205 The whole user memory access is reduced to 10 x86 machine instructions.
210  > objdump --disassemble --section=.fixup vmlinux
218  > objdump --full-contents --section=__ex_table vmlinux
240   3:      movl $-14,%eax
257 the original assembly code: > 3:      movl $-14,%eax
287 #. kernelmode_fixup_or_oops() calls fixup_exception() (regs->eip == c017e7a5);
295 #. a) EAX becomes -EFAULT (== -14)
303 we set EAX to -EFAULT in the exception handler code. Well, the
305 successful, -EFAULT on failure. Our original code did not test this
307 return -EFAULT. GCC selected EAX to return this value.
315 Things changed when 64-bit support was added to x86 Linux. Rather than
317 from 32-bits to 64 bits, a clever trick was used to store addresses
323           .long (from) - .
324           .long (to) - .
326 and the C-code that uses these values converts back to absolute addresses
331 		return (unsigned long)&x->insn + x->insn;
335 This is also 32-bits wide and contains a third relative function
343      entry->insn. It is used to distinguish page faults from machine