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DrXiaoDrXiao
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Support Arm dynamic linking
This commit implements dynamic linking for the Arm target so that the compiler has the ability to generate dynamically linked program to use the external C library such as glibc. It includes the following changes: - Modify arm.mk to make the compiled executable use hard-float ABI. - Add a new header named 'c.h' that only includes declaration of C standard functions. If using dynamic linking mode, the compiler will use this file to generate C functions for the compiled program. - Generate dynamically linked program by adding the following data: - Dynamic sections such such as '.interp', '.plt', '.got' and so on. - Additional program headers and section headers. - Make the entire compilation process able to compile the functions without implementation, which are considered to be external functions. - Add a new input argument "--dynlink" to enable the dynamic linking mode. - Improve the build system to build the compiler under the dynamic linking mode by the command "make DYNLINK=1". - Stop the build process if the target architecture and the mode are RISC-V and dynamic linking, respectively, because this commit only implements for the Arm architecture.
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15 files changed

+910
-178
lines changed

15 files changed

+910
-178
lines changed

‎Makefile‎

Lines changed: 18 additions & 5 deletions
Original file line numberDiff line numberDiff line change
@@ -43,6 +43,19 @@ HOST_ARCH = $(shell arch 2>/dev/null)
4343
SRCDIR := $(shell find src -type d)
4444
LIBDIR := $(shell find lib -type d)
4545

46+
BUILTIN_LIBC ?= c.c
47+
STAGE0_FLAGS ?= --dump-ir
48+
STAGE1_FLAGS ?=
49+
ifeq ($(DYNLINK),1)
50+
ifeq ($(ARCH),riscv)
51+
# TODO: implement dynamic linking for RISC-V.
52+
$(error "Dynamic linking mode is not implemented for RISC-V")
53+
endif
54+
BUILTIN_LIBC := c.h
55+
STAGE0_FLAGS += --dynlink
56+
STAGE1_FLAGS += --dynlink
57+
endif
58+
4659
SRCS := $(wildcard $(patsubst %,%/main.c, $(SRCDIR)))
4760
OBJS := $(SRCS:%.c=$(OUT)/%.o)
4861
deps := $(OBJS:%.o=%.o.d)
@@ -72,7 +85,7 @@ config:
7285

7386
$(OUT)/tests/%.elf: tests/%.c $(OUT)/$(STAGE0)
7487
$(VECHO) " SHECC\t$@\n"
75-
$(Q)$(OUT)/$(STAGE0) --dump-ir -o $@ $< > $(basename $@).log ; \
88+
$(Q)$(OUT)/$(STAGE0) $(STAGE0_FLAGS) -o $@ $< > $(basename $@).log ; \
7689
chmod +x $@ ; $(PRINTF) "Running $@ ...\n"
7790
$(Q)$(TARGET_EXEC) $@ && $(call pass)
7891

@@ -122,9 +135,9 @@ $(OUT)/norm-lf: tools/norm-lf.c
122135
$(VECHO) " CC+LD\t$@\n"
123136
$(Q)$(CC) $(CFLAGS) -o $@ $^
124137

125-
$(OUT)/libc.inc: $(OUT)/inliner $(OUT)/norm-lf $(LIBDIR)/c.c
138+
$(OUT)/libc.inc: $(OUT)/inliner $(OUT)/norm-lf $(LIBDIR)/$(BUILTIN_LIBC)
126139
$(VECHO) " GEN\t$@\n"
127-
$(Q)$(OUT)/norm-lf $(LIBDIR)/c.c $(OUT)/c.normalized.c
140+
$(Q)$(OUT)/norm-lf $(LIBDIR)/$(BUILTIN_LIBC) $(OUT)/c.normalized.c
128141
$(Q)$(OUT)/inliner $(OUT)/c.normalized.c $@
129142
$(Q)$(RM) $(OUT)/c.normalized.c
130143

@@ -143,12 +156,12 @@ $(OUT)/$(STAGE0)-sanitizer: $(OUT)/libc.inc $(OBJS)
143156
$(OUT)/$(STAGE1): $(OUT)/$(STAGE0)
144157
$(Q)$(STAGE1_CHECK_CMD)
145158
$(VECHO) " SHECC\t$@\n"
146-
$(Q)$(OUT)/$(STAGE0) --dump-ir -o $@ $(SRCDIR)/main.c > $(OUT)/shecc-stage1.log
159+
$(Q)$(OUT)/$(STAGE0) $(STAGE0_FLAGS) -o $@ $(SRCDIR)/main.c > $(OUT)/shecc-stage1.log
147160
$(Q)chmod a+x $@
148161

149162
$(OUT)/$(STAGE2): $(OUT)/$(STAGE1)
150163
$(VECHO) " SHECC\t$@\n"
151-
$(Q)$(TARGET_EXEC) $(OUT)/$(STAGE1) -o $@ $(SRCDIR)/main.c
164+
$(Q)$(TARGET_EXEC) $(OUT)/$(STAGE1) $(STAGE1_FLAGS) -o $@ $(SRCDIR)/main.c
152165

153166
bootstrap: $(OUT)/$(STAGE2)
154167
$(Q)chmod 775 $(OUT)/$(STAGE2)

‎lib/c.h‎

Lines changed: 50 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,50 @@
1+
/*
2+
* shecc - Self-Hosting and Educational C Compiler.
3+
*
4+
* shecc is freely redistributable under the BSD 2 clause license. See the
5+
* file "LICENSE" for information on usage and redistribution of this file.
6+
*/
7+
8+
#pragma once
9+
/* Declarations of C standard library functions */
10+
11+
#define NULL 0
12+
13+
#define bool _Bool
14+
#define true 1
15+
#define false 0
16+
17+
/* va_list support for variadic functions */
18+
typedef int *va_list;
19+
20+
/* File I/O */
21+
typedef int FILE;
22+
FILE *fopen(char *filename, char *mode);
23+
int fclose(FILE *stream);
24+
int fgetc(FILE *stream);
25+
char *fgets(char *str, int n, FILE *stream);
26+
int fputc(int c, FILE *stream);
27+
28+
/* string-related functions */
29+
int strlen(char *str);
30+
int strcmp(char *s1, char *s2);
31+
int strncmp(char *s1, char *s2, int len);
32+
char *strcpy(char *dest, char *src);
33+
char *strncpy(char *dest, char *src, int len);
34+
char *memcpy(char *dest, char *src, int count);
35+
int memcmp(void *s1, void *s2, int n);
36+
void *memset(void *s, int c, int n);
37+
38+
/* formatted output string */
39+
int printf(char *str, ...);
40+
int sprintf(char *buffer, char *str, ...);
41+
int snprintf(char *buffer, int n, char *str, ...);
42+
43+
/* Terminating program */
44+
void exit(int exit_code);
45+
void abort(void);
46+
47+
/* Dynamic memory allocation/deallocation functions */
48+
void *malloc(int size);
49+
void *calloc(int n, int size);
50+
void free(void *ptr);

‎mk/arm.mk‎

Lines changed: 7 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -5,5 +5,11 @@ ARCH_DEFS = \
55
\#pragma once\n$\
66
\#define ARCH_PREDEFINED \"__arm__\" /* defined by GNU C and RealView */\n$\
77
\#define ELF_MACHINE 0x28 /* up to ARMv7/Aarch32 */\n$\
8-
\#define ELF_FLAGS 0x5000200\n$\
8+
\#define ELF_FLAGS 0x5000400\n$\
9+
\#define DYN_LINKER \"/lib/ld-linux-armhf.so.3\"\n$\
10+
\#define LIBC_SO \"libc.so.6\"\n$\
11+
\#define PLT_FIXUP_SIZE 20\n$\
12+
\#define PLT_ENT_SIZE 12\n$\
13+
\#define R_ARCH_JUMP_SLOT 0x16\n$\
914
"
15+
RUNNER_LD_PREFIX=-L /usr/arm-linux-gnueabihf/

‎mk/common.mk‎

Lines changed: 3 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -36,6 +36,9 @@ ifneq ($(HOST_ARCH),$(ARCH_NAME))
3636

3737
# Generate the path to the architecture-specific qemu
3838
TARGET_EXEC = $(shell which $(ARCH_RUNNER))
39+
ifeq ($(DYNLINK),1)
40+
TARGET_EXEC += $(RUNNER_LD_PREFIX)
41+
endif
3942
endif
4043
export TARGET_EXEC
4144

‎mk/riscv.mk‎

Lines changed: 8 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -7,4 +7,12 @@ ARCH_DEFS = \
77
\#define ARCH_PREDEFINED \"__riscv\" /* Older versions of the GCC toolchain defined __riscv__ */\n$\
88
\#define ELF_MACHINE 0xf3\n$\
99
\#define ELF_FLAGS 0\n$\
10+
\#define DYN_LINKER \"/lib/ld-linux.so.3\"\n$\
11+
\#define LIBC_SO \"libc.so.6\"\n$\
12+
\#define PLT_FIXUP_SIZE 20\n$\
13+
\#define PLT_ENT_SIZE 12\n$\
14+
\#define R_ARCH_JUMP_SLOT 0x5\n$\
1015
"
16+
17+
# TODO: Set this variable for RISC-V architecture
18+
RUNNER_LD_PREFIX=

‎src/arm-codegen.c‎

Lines changed: 144 additions & 40 deletions
Original file line numberDiff line numberDiff line change
@@ -139,10 +139,18 @@ void update_elf_offset(ph2_ir_t *ph2_ir)
139139

140140
void cfg_flatten(void)
141141
{
142-
func_t *func = find_func("__syscall");
143-
func->bbs->elf_offset = 48; /* offset of start + branch + exit in codegen */
142+
func_t *func;
143+
144+
if (dynlink)
145+
elf_offset =
146+
88; /* offset of __libc_start_main + main_wrapper in codegen */
147+
else {
148+
func = find_func("__syscall");
149+
func->bbs->elf_offset = 48; /* offset of start + exit in codegen */
150+
elf_offset =
151+
84; /* offset of start + branch + exit + syscall in codegen */
152+
}
144153

145-
elf_offset = 84; /* offset of start + branch + exit + syscall in codegen */
146154
GLOBAL_FUNC->bbs->elf_offset = elf_offset;
147155

148156
for (ph2_ir_t *ph2_ir = GLOBAL_FUNC->bbs->ph2_ir_list.head; ph2_ir;
@@ -151,7 +159,10 @@ void cfg_flatten(void)
151159
}
152160

153161
/* prepare 'argc' and 'argv', then proceed to 'main' function */
154-
elf_offset += 32; /* 6 insns for main call + 2 for exit */
162+
if (dynlink)
163+
elf_offset += 28;
164+
else
165+
elf_offset += 32; /* 6 insns for main call + 2 for exit */
155166

156167
for (func = FUNC_LIST.head; func; func = func->next) {
157168
/* Skip function declarations without bodies */
@@ -294,7 +305,16 @@ void emit_ph2_ir(ph2_ir_t *ph2_ir)
294305
return;
295306
case OP_call:
296307
func = find_func(ph2_ir->func_name);
297-
emit(__bl(__AL, func->bbs->elf_offset - elf_code->size));
308+
if (func->bbs)
309+
ofs = func->bbs->elf_offset - elf_code->size;
310+
else if (dynlink)
311+
ofs = (dynamic_sections.elf_plt_start + func->plt_offset) -
312+
(elf_code_start + elf_code->size);
313+
else {
314+
printf("The '%s' function is not implemented\n", ph2_ir->func_name);
315+
abort();
316+
}
317+
emit(__bl(__AL, ofs));
298318
return;
299319
case OP_load_data_address:
300320
emit(__movw(__AL, rd, ph2_ir->src0 + elf_data_start));
@@ -306,7 +326,14 @@ void emit_ph2_ir(ph2_ir_t *ph2_ir)
306326
return;
307327
case OP_address_of_func:
308328
func = find_func(ph2_ir->func_name);
309-
ofs = elf_code_start + func->bbs->elf_offset;
329+
if (func->bbs)
330+
ofs = elf_code_start + func->bbs->elf_offset;
331+
else if (dynlink)
332+
ofs = dynamic_sections.elf_plt_start + func->plt_offset;
333+
else {
334+
printf("The '%s' function is not implemented\n", ph2_ir->func_name);
335+
abort();
336+
}
310337
emit(__movw(__AL, __r8, ofs));
311338
emit(__movt(__AL, __r8, ofs));
312339
emit(__sw(__AL, __r8, rn, 0));
@@ -470,39 +497,76 @@ void emit_ph2_ir(ph2_ir_t *ph2_ir)
470497
}
471498
}
472499

500+
void plt_generate(void);
473501
void code_generate(void)
474502
{
475-
elf_data_start = elf_code_start + elf_offset;
476-
elf_rodata_start = elf_data_start + elf_data->size;
477-
elf_bss_start = elf_rodata_start + elf_rodata->size;
503+
if (dynlink) {
504+
plt_generate();
505+
/* Call __libc_start_main() */
506+
emit(__mov_i(__AL, __r11, 0));
507+
emit(__mov_i(__AL, __lr, 0));
508+
emit(__pop_word(__AL, __r1));
509+
emit(__mov_r(__AL, __r2, __sp));
510+
emit(__push_reg(__AL, __r2));
511+
emit(__push_reg(__AL, __r0));
512+
emit(__mov_i(__AL, __r12, 0));
513+
emit(__push_reg(__AL, __r12));
514+
515+
int main_wrapper_offset = elf_code->size + 28;
516+
emit(__movw(__AL, __r0, elf_code_start + main_wrapper_offset));
517+
emit(__movt(__AL, __r0, elf_code_start + main_wrapper_offset));
518+
emit(__mov_i(__AL, __r3, 0));
519+
emit(__bl(__AL, (dynamic_sections.elf_plt_start + PLT_FIXUP_SIZE) -
520+
(elf_code_start + elf_code->size)));
521+
/* Call '_exit' (syscall) to terminate the program if __libc_start_main
522+
* returns. */
523+
emit(__mov_i(__AL, __r0, 127));
524+
emit(__mov_i(__AL, __r7, 1));
525+
emit(__svc());
478526

479-
/* start */
527+
/* If the compiled program is dynamic linking, the starting
528+
* point of 'main_wrapper' is located here.
529+
*
530+
* Push the contents of r4-r11 and lr onto stack.
531+
* Preserve 'argc' and 'argv' for the 'main' function.
532+
*/
533+
emit(__stmdb(__AL, 1, __sp, 0x4FF0));
534+
emit(__mov_r(__AL, __r9, __r0));
535+
emit(__mov_r(__AL, __r10, __r1));
536+
}
537+
/* For both static and dynamic linking, we need to set up the stack
538+
* and call the main function.
539+
*/
480540
emit(__movw(__AL, __r8, GLOBAL_FUNC->stack_size));
481541
emit(__movt(__AL, __r8, GLOBAL_FUNC->stack_size));
482542
emit(__sub_r(__AL, __sp, __sp, __r8));
483543
emit(__mov_r(__AL, __r12, __sp));
484-
emit(__bl(__AL, GLOBAL_FUNC->bbs->elf_offset - elf_code->size));
485-
/* After global init, jump to main preparation */
486-
emit(__b(__AL, 56)); /* PC+8: skip exit (24) + syscall (36) + ret (4) - 8 */
487544

488-
/* exit */
489-
emit(__movw(__AL, __r8, GLOBAL_FUNC->stack_size));
490-
emit(__movt(__AL, __r8, GLOBAL_FUNC->stack_size));
491-
emit(__add_r(__AL, __sp, __sp, __r8));
492-
emit(__mov_r(__AL, __r0, __r0));
493-
emit(__mov_i(__AL, __r7, 1));
494-
emit(__svc());
495-
496-
/* syscall */
497-
emit(__mov_r(__AL, __r7, __r0));
498-
emit(__mov_r(__AL, __r0, __r1));
499-
emit(__mov_r(__AL, __r1, __r2));
500-
emit(__mov_r(__AL, __r2, __r3));
501-
emit(__mov_r(__AL, __r3, __r4));
502-
emit(__mov_r(__AL, __r4, __r5));
503-
emit(__mov_r(__AL, __r5, __r6));
504-
emit(__svc());
505-
emit(__bx(__AL, __lr));
545+
if (!dynlink) {
546+
emit(__bl(__AL, GLOBAL_FUNC->bbs->elf_offset - elf_code->size));
547+
/* After global init, jump to main preparation */
548+
emit(__b(__AL,
549+
56)); /* PC+8: skip exit (24) + syscall (36) + ret (4) - 8 */
550+
551+
/* exit - only for static linking */
552+
emit(__movw(__AL, __r8, GLOBAL_FUNC->stack_size));
553+
emit(__movt(__AL, __r8, GLOBAL_FUNC->stack_size));
554+
emit(__add_r(__AL, __sp, __sp, __r8));
555+
emit(__mov_r(__AL, __r0, __r0));
556+
emit(__mov_i(__AL, __r7, 1));
557+
emit(__svc());
558+
559+
/* syscall */
560+
emit(__mov_r(__AL, __r7, __r0));
561+
emit(__mov_r(__AL, __r0, __r1));
562+
emit(__mov_r(__AL, __r1, __r2));
563+
emit(__mov_r(__AL, __r2, __r3));
564+
emit(__mov_r(__AL, __r3, __r4));
565+
emit(__mov_r(__AL, __r4, __r5));
566+
emit(__mov_r(__AL, __r5, __r6));
567+
emit(__svc());
568+
emit(__bx(__AL, __lr));
569+
}
506570

507571
ph2_ir_t *ph2_ir;
508572
for (ph2_ir = GLOBAL_FUNC->bbs->ph2_ir_list.head; ph2_ir;
@@ -511,20 +575,60 @@ void code_generate(void)
511575

512576
/* prepare 'argc' and 'argv', then proceed to 'main' function */
513577
if (MAIN_BB) {
514-
emit(__movw(__AL, __r8, GLOBAL_FUNC->stack_size));
515-
emit(__movt(__AL, __r8, GLOBAL_FUNC->stack_size));
516-
emit(__add_r(__AL, __r8, __r12, __r8));
517-
emit(__lw(__AL, __r0, __r8, 0));
518-
emit(__add_i(__AL, __r1, __r8, 4));
519-
emit(__bl(__AL, MAIN_BB->elf_offset - elf_code->size));
578+
if (dynlink) {
579+
emit(__mov_r(__AL, __r0, __r9));
580+
emit(__mov_r(__AL, __r1, __r10));
581+
/* Call the main function.
582+
*
583+
* After the main function returns, the following
584+
* instructions restore the registers r4-r11 and
585+
* return control to __libc_start_main via the
586+
* preserved lr.
587+
*/
588+
emit(__bl(__AL, MAIN_BB->elf_offset - elf_code->size));
589+
emit(__movw(__AL, __r8, GLOBAL_FUNC->stack_size));
590+
emit(__movt(__AL, __r8, GLOBAL_FUNC->stack_size));
591+
emit(__add_r(__AL, __sp, __sp, __r8));
592+
emit(__ldm(__AL, 1, __sp, 0x8FF0));
593+
} else {
594+
emit(__movw(__AL, __r8, GLOBAL_FUNC->stack_size));
595+
emit(__movt(__AL, __r8, GLOBAL_FUNC->stack_size));
596+
emit(__add_r(__AL, __r8, __r12, __r8));
597+
emit(__lw(__AL, __r0, __r8, 0));
598+
emit(__add_i(__AL, __r1, __r8, 4));
520599

521-
/* exit with main's return value - r0 already has the return value */
522-
emit(__mov_i(__AL, __r7, 1));
523-
emit(__svc());
600+
/* Call main function, and call '_exit' syscall to
601+
* terminate the program. */
602+
emit(__bl(__AL, MAIN_BB->elf_offset - elf_code->size));
603+
604+
/* exit with main's return value - r0 already has the
605+
* return value */
606+
emit(__mov_i(__AL, __r7, 1));
607+
emit(__svc());
608+
}
524609
}
525610

526611
for (int i = 0; i < ph2_ir_idx; i++) {
527612
ph2_ir = PH2_IR_FLATTEN[i];
528613
emit_ph2_ir(ph2_ir);
529614
}
530615
}
616+
617+
void plt_generate(void)
618+
{
619+
int addr_of_got = dynamic_sections.elf_got_start + PTR_SIZE * 2;
620+
int end = dynamic_sections.plt_size - PLT_FIXUP_SIZE;
621+
elf_write_int(dynamic_sections.elf_plt, __push_reg(__AL, __lr));
622+
elf_write_int(dynamic_sections.elf_plt, __movw(__AL, __r10, addr_of_got));
623+
elf_write_int(dynamic_sections.elf_plt, __movt(__AL, __r10, addr_of_got));
624+
elf_write_int(dynamic_sections.elf_plt, __mov_r(__AL, __lr, __r10));
625+
elf_write_int(dynamic_sections.elf_plt, __lw(__AL, __pc, __lr, 0));
626+
for (int i = 0; i * PLT_ENT_SIZE < end; i++) {
627+
addr_of_got = dynamic_sections.elf_got_start + PTR_SIZE * (i + 3);
628+
elf_write_int(dynamic_sections.elf_plt,
629+
__movw(__AL, __r12, addr_of_got));
630+
elf_write_int(dynamic_sections.elf_plt,
631+
__movt(__AL, __r12, addr_of_got));
632+
elf_write_int(dynamic_sections.elf_plt, __lw(__AL, __pc, __r12, 0));
633+
}
634+
}

‎src/arm.c‎

Lines changed: 10 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -357,6 +357,16 @@ int __ldm(arm_cond_t cond, int w, arm_reg rn, int reg_list)
357357
return arm_encode(cond, arm_ldm + (0x2 << 6) + (w << 1), rn, 0, reg_list);
358358
}
359359

360+
int __push_reg(arm_cond_t cond, arm_reg rt)
361+
{
362+
return arm_encode(cond, (0x5 << 4) | 0x2, 0xd, rt, 0x4);
363+
}
364+
365+
int __pop_word(arm_cond_t cond, arm_reg rt)
366+
{
367+
return arm_encode(cond, (0x4 << 4) | 0x9, 0xd, rt, 0x4);
368+
}
369+
360370
int __b(arm_cond_t cond, int ofs)
361371
{
362372
int o = (ofs - 8) >> 2;

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