1.伪指令概述
as支持非常多的伪指令，例如macro,if,rept,struct,include等等，这些伪指令对于汇编器处理能力的扩充非常重要,可以减少编程的工作量。从前面列出的伪指令来看，as支持宏汇编，条件汇编，以及循环、结构和文件包含等重要功能。
2.伪指令表初始化
as初始化的时候先建立伪指令表，便于迅速查找伪指令.
2.1 pobegin
main->read_begin->pobegin
static void
pobegin (void)
{
po_hash = hash_new ();
/* Do the target-specific pseudo ops. */
pop_table_name = "md";
md_pop_insert ();
/* Now object specific. Skip any that were in the target table. */
pop_table_name = "obj";
pop_override_ok = 1;
obj_pop_insert ();
/* Now portable ones. Skip any that we've seen already. */
pop_table_name = "standard";
pop_insert (potable);
#ifdef TARGET_USE_CFIPOP
pop_table_name = "cfi";
pop_override_ok = 1;
cfi_pop_insert ();
#endif
}
po_hash显然用于存放所有伪指令的hash表，使用hash数据结构加速查找伪指令的速度.
2.2 md_pop_insert
main->read_begin->pobegin
{
/* Do the target-specific pseudo ops. */
pop_table_name = "md";
md_pop_insert ();
}
md_pop_insert初始化平台相关伪指令.
#ifndef md_pop_insert
#define md_pop_insert() pop_insert(md_pseudo_table)
#endif
md_pseudo_table在gas/config/tc-i386.c中
const pseudo_typeS md_pseudo_table[] =
{
#if !defined(OBJ_AOUT) && !defined(USE_ALIGN_PTWO)
{"align", s_align_bytes, 0},
#else
{"align", s_align_ptwo, 0},
#endif
{"arch", set_cpu_arch, 0},
#ifndef I386COFF
{"bss", s_bss, 0},
#endif
{"ffloat", float_cons, 'f'},
{"dfloat", float_cons, 'd'},
{"tfloat", float_cons, 'x'},
{"value", cons, 2},
{"slong", signed_cons, 4},
{"noopt", s_ignore, 0},
{"optim", s_ignore, 0},
{"code16gcc", set_16bit_gcc_code_flag, CODE_16BIT},
{"code16", set_code_flag, CODE_16BIT},
{"code32", set_code_flag, CODE_32BIT},
{"code64", set_code_flag, CODE_64BIT},
{"intel_syntax", set_intel_syntax, 1},
{"att_syntax", set_intel_syntax, 0},
#if defined (OBJ_ELF) || defined (OBJ_MAYBE_ELF)
{"largecomm", handle_large_common, 0},
#else
{"file", (void (*) (int)) dwarf2_directive_file, 0},
{"loc", dwarf2_directive_loc, 0},
{"loc_mark_labels", dwarf2_directive_loc_mark_labels, 0},
#endif
#ifdef TE_PE
{"secrel32", pe_directive_secrel, 0},
#endif
{0, 0, 0}
};
pseudo_typeS数据结构类型是
struct _pseudo_type
{
/* assembler mnemonic, lower case, no '.' */
const char *poc_name;
/* Do the work */
void (*poc_handler) (int);
/* Value to pass to handler */
int poc_val;
};
typedef struct _pseudo_type pseudo_typeS;
main->read_begin->pobegin->md_pop_insert->pop_insert
void
pop_insert (const pseudo_typeS *table)
{
const char *errtxt;
const pseudo_typeS *pop;
for (pop = table; pop->poc_name; pop++)
{
errtxt = hash_insert (po_hash, pop->poc_name, (char *) pop);//插入hash表
if (errtxt ////出错，
&& (!pop_override_ok //并且不允许重复定义
|| strcmp (errtxt, "exists")))//或者错误信息不是已存在该伪指令
as_fatal (_("error constructing %s pseudo-op table: %s"), pop_table_name,
errtxt);//打印出现信息
}
}
2.3 obj_pop_insert
main->read_begin->pobegin
{
/* Now object specific. Skip any that were in the target table. */
pop_table_name = "obj";
pop_override_ok = 1;//<<<如果伪指令重复定义，不报错
obj_pop_insert ();
}
obj_pop_insert初始化目标文件相关指令，目标文件一般是elf.
#ifndef obj_pop_insert
#define obj_pop_insert() elf_pop_insert()
#endif
main->read_begin->pobegin->obj_pop_insert->elf_pop_insert
void
elf_pop_insert (void)
{
pop_insert (elf_pseudo_table);
if (ECOFF_DEBUGGING)
pop_insert (ecoff_debug_pseudo_table);
}
下面是elf_pseudo_table的定义
static const pseudo_typeS elf_pseudo_table[] =
{
{"comm", obj_elf_common, 0},
{"common", obj_elf_common, 1},
{"ident", obj_elf_ident, 0},
{"lcomm", obj_elf_lcomm, 0},
{"local", obj_elf_local, 0},
{"previous", obj_elf_previous, 0},
{"section", obj_elf_section, 0},
{"section.s", obj_elf_section, 0},
{"sect", obj_elf_section, 0},
{"sect.s", obj_elf_section, 0},
{"pushsection", obj_elf_section, 1},
{"popsection", obj_elf_popsection, 0},
{"size", obj_elf_size, 0},
{"type", obj_elf_type, 0},
{"version", obj_elf_version, 0},
{"weak", obj_elf_weak, 0},
/* These define symbol visibility. */
{"internal", obj_elf_visibility, STV_INTERNAL},
{"hidden", obj_elf_visibility, STV_HIDDEN},
{"protected", obj_elf_visibility, STV_PROTECTED},
/* These are used for stabs-in-elf configurations. */
{"line", obj_elf_line, 0},
/* This is a GNU extension to handle symbol versions. */
{"symver", obj_elf_symver, 0},
/* A GNU extension to change subsection only. */
{"subsection", obj_elf_subsection, 0},
/* These are GNU extensions to aid in garbage collecting C++ vtables. */
{"vtable_inherit", (void (*) (int)) &obj_elf_vtable_inherit, 0},
{"vtable_entry", (void (*) (int)) &obj_elf_vtable_entry, 0},
/* These are used for dwarf. */
{"2byte", cons, 2},
{"4byte", cons, 4},
{"8byte", cons, 8},
/* These are used for dwarf2. */
{ "file", (void (*) (int)) dwarf2_directive_file, 0 },
{ "loc", dwarf2_directive_loc, 0 },
{ "loc_mark_labels", dwarf2_directive_loc_mark_labels, 0 },
/* We need to trap the section changing calls to handle .previous. */
{"data", obj_elf_data, 0},
{"offset", obj_elf_struct, 0},
{"struct", obj_elf_struct, 0},
{"text", obj_elf_text, 0},
{"tls_common", obj_elf_tls_common, 0},
/* End sentinel. */
{NULL, NULL, 0},
};
2.4初始化potable
main->read_begin->pobegin
{
/* Now portable ones. Skip any that we've seen already. */
pop_table_name = "standard";
pop_insert (potable);
}
potable包括所有的可移植伪指令，这些伪指令可能和前面的指令重复，但是pop_override_ok已设置，不会有问题。
显然，potable包含了绝大部分伪指令。
static const pseudo_typeS potable[] = {
{"abort", s_abort, 0},
{"align", s_align_ptwo, 0},
{"altmacro", s_altmacro, 1},
{"ascii", stringer, 0},
{"asciz", stringer, 1},
{"balign", s_align_bytes, 0},
{"balignw", s_align_bytes, -2},
{"balignl", s_align_bytes, -4},
/* block */
{"byte", cons, 1},
{"comm", s_comm, 0},
{"common", s_mri_common, 0},
{"common.s", s_mri_common, 1},
{"data", s_data, 0},
{"dc", cons, 2},
#ifdef TC_ADDRESS_BYTES
{"dc.a", cons, 0},
#endif
{"dc.b", cons, 1},
{"dc.d", float_cons, 'd'},
{"dc.l", cons, 4},
{"dc.s", float_cons, 'f'},
{"dc.w", cons, 2},
{"dc.x", float_cons, 'x'},
{"dcb", s_space, 2},
{"dcb.b", s_space, 1},
{"dcb.d", s_float_space, 'd'},
{"dcb.l", s_space, 4},
{"dcb.s", s_float_space, 'f'},
{"dcb.w", s_space, 2},
{"dcb.x", s_float_space, 'x'},
{"ds", s_space, 2},
{"ds.b", s_space, 1},
{"ds.d", s_space, 8},
{"ds.l", s_space, 4},
{"ds.p", s_space, 12},
{"ds.s", s_space, 4},
{"ds.w", s_space, 2},
{"ds.x", s_space, 12},
{"debug", s_ignore, 0},
#ifdef S_SET_DESC
{"desc", s_desc, 0},
#endif
/* dim */
{"double", float_cons, 'd'},
/* dsect */
{"eject", listing_eject, 0}, /* Formfeed listing. */
{"else", s_else, 0},
{"elsec", s_else, 0},
{"elseif", s_elseif, (int) O_ne},
{"end", s_end, 0},
{"endc", s_endif, 0},
{"endfunc", s_func, 1},
{"endif", s_endif, 0},
{"endm", s_bad_end, 0},
{"endr", s_bad_end, 1},
/* endef */
{"equ", s_set, 0},
{"equiv", s_set, 1},
{"eqv", s_set, -1},
{"err", s_err, 0},
{"error", s_errwarn, 1},
{"exitm", s_mexit, 0},
/* extend */
{"extern", s_ignore, 0}, /* We treat all undef as ext. */
{"appfile", s_app_file, 1},
{"appline", s_app_line, 1},
{"fail", s_fail, 0},
{"file", s_app_file, 0},
{"fill", s_fill, 0},
{"float", float_cons, 'f'},
{"format", s_ignore, 0},
{"func", s_func, 0},
{"global", s_globl, 0},
{"globl", s_globl, 0},
#ifdef OBJ_ELF
{"gnu_attribute", s_gnu_attribute, 0},
#endif
{"hword", cons, 2},
{"if", s_if, (int) O_ne},
{"ifb", s_ifb, 1},
{"ifc", s_ifc, 0},
{"ifdef", s_ifdef, 0},
{"ifeq", s_if, (int) O_eq},
{"ifeqs", s_ifeqs, 0},
{"ifge", s_if, (int) O_ge},
{"ifgt", s_if, (int) O_gt},
{"ifle", s_if, (int) O_le},
{"iflt", s_if, (int) O_lt},
{"ifnb", s_ifb, 0},
{"ifnc", s_ifc, 1},
{"ifndef", s_ifdef, 1},
{"ifne", s_if, (int) O_ne},
{"ifnes", s_ifeqs, 1},
{"ifnotdef", s_ifdef, 1},
{"incbin", s_incbin, 0},
{"include", s_include, 0},
{"int", cons, 4},
{"irp", s_irp, 0},
{"irep", s_irp, 0},
{"irpc", s_irp, 1},
{"irepc", s_irp, 1},
{"lcomm", s_lcomm, 0},
{"lflags", listing_flags, 0}, /* Listing flags. */
{"linefile", s_app_line, 0},
{"linkonce", s_linkonce, 0},
{"list", listing_list, 1}, /* Turn listing on. */
{"llen", listing_psize, 1},
{"long", cons, 4},
{"lsym", s_lsym, 0},
{"macro", s_macro, 0},
{"mexit", s_mexit, 0},
{"mri", s_mri, 0},
{".mri", s_mri, 0}, /* Special case so .mri works in MRI mode. */
{"name", s_ignore, 0},
{"noaltmacro", s_altmacro, 0},
{"noformat", s_ignore, 0},
{"nolist", listing_list, 0}, /* Turn listing off. */
{"nopage", listing_nopage, 0},
{"octa", cons, 16},
{"offset", s_struct, 0},
{"org", s_org, 0},
{"p2align", s_align_ptwo, 0},
{"p2alignw", s_align_ptwo, -2},
{"p2alignl", s_align_ptwo, -4},
{"page", listing_eject, 0},
{"plen", listing_psize, 0},
{"print", s_print, 0},
{"psize", listing_psize, 0}, /* Set paper size. */
{"purgem", s_purgem, 0},
{"quad", cons, 8},
{"reloc", s_reloc, 0},
{"rep", s_rept, 0},
{"rept", s_rept, 0},
{"rva", s_rva, 4},
{"sbttl", listing_title, 1}, /* Subtitle of listing. */
/* scl */
/* sect */
{"set", s_set, 0},
{"short", cons, 2},
{"single", float_cons, 'f'},
/* size */
{"space", s_space, 0},
{"skip", s_space, 0},
{"sleb128", s_leb128, 1},
{"spc", s_ignore, 0},
{"stabd", s_stab, 'd'},
{"stabn", s_stab, 'n'},
{"stabs", s_stab, 's'},
{"string", stringer, 1},
{"struct", s_struct, 0},
/* tag */
{"text", s_text, 0},
/* This is for gcc to use. It's only just been added (2/94), so gcc
won't be able to use it for a while -- probably a year or more.
But once this has been released, check with gcc maintainers
before deleting it or even changing the spelling. */
{"this_GCC_requires_the_GNU_assembler", s_ignore, 0},
/* If we're folding case -- done for some targets, not necessarily
all -- the above string in an input file will be converted to
this one. Match it either way... */
{"this_gcc_requires_the_gnu_assembler", s_ignore, 0},
{"title", listing_title, 0}, /* Listing title. */
{"ttl", listing_title, 0},
/* type */
{"uleb128", s_leb128, 0},
/* use */
/* val */
{"xcom", s_comm, 0},
{"xdef", s_globl, 0},
{"xref", s_ignore, 0},
{"xstabs", s_xstab, 's'},
{"warning", s_errwarn, 0},
{"weakref", s_weakref, 0},
{"word", cons, 2},
{"zero", s_space, 0},
{NULL, NULL, 0} /* End sentinel. */
};
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