Gcc Compile C Prog

April 29, 2025

分析代码

os: Linux Mint 22.1

hello.c

#include <stdio.h>
int main(void){
    printf("hello world");
}

strace 追踪编译流程

strace -t -f -o hello.log -e trace=execve -s 2000 gcc -o hello hello.c

All execve() system calls during compilation, showing how GCC orchestrates the build process.

hello.log 内容

20029 13:48:52 execve("/usr/bin/gcc", ["gcc", "-o", "hello", "hello.c"], 0x7ffd60d08358 /* 65 vars */) = 0
20034 13:48:52 execve("/usr/libexec/gcc/x86_64-linux-gnu/13/cc1", ["/usr/libexec/gcc/x86_64-linux-gnu/13/cc1", "-quiet", "-imultiarch", "x86_64-linux-gnu", "hello.c", "-quiet", "-dumpbase", "hello.c", "-dumpbase-ext", ".c", "-mtune=generic", "-march=x86-64", "-fasynchronous-unwind-tables", "-fstack-protector-strong", "-Wformat", "-Wformat-security", "-fstack-clash-protection", "-fcf-protection", "-o", "/tmp/ccLfEVyN.s"], 0x7d14db0 /* 70 vars */) = 0
20034 13:48:53 +++ exited with 0 +++
20029 13:48:53 --- SIGCHLD {si_signo=SIGCHLD, si_code=CLD_EXITED, si_pid=20034, si_uid=1000, si_status=0, si_utime=3 /* 0.03 s */, si_stime=17 /* 0.17 s */} ---
20036 13:48:53 execve("/usr/local/sbin/as", ["as", "--64", "-o", "/tmp/ccGZrdFz.o", "/tmp/ccLfEVyN.s"], 0x7d14db0 /* 70 vars */) = -1 ENOENT (No such file or directory)
20036 13:48:53 execve("/usr/local/bin/as", ["as", "--64", "-o", "/tmp/ccGZrdFz.o", "/tmp/ccLfEVyN.s"], 0x7d14db0 /* 70 vars */) = -1 ENOENT (No such file or directory)
20036 13:48:53 execve("/usr/sbin/as", ["as", "--64", "-o", "/tmp/ccGZrdFz.o", "/tmp/ccLfEVyN.s"], 0x7d14db0 /* 70 vars */) = -1 ENOENT (No such file or directory)
20036 13:48:53 execve("/usr/bin/as", ["as", "--64", "-o", "/tmp/ccGZrdFz.o", "/tmp/ccLfEVyN.s"], 0x7d14db0 /* 70 vars */) = 0
20036 13:48:53 +++ exited with 0 +++
20029 13:48:53 --- SIGCHLD {si_signo=SIGCHLD, si_code=CLD_EXITED, si_pid=20036, si_uid=1000, si_status=0, si_utime=0, si_stime=1 /* 0.01 s */} ---
20037 13:48:53 execve("/usr/libexec/gcc/x86_64-linux-gnu/13/collect2", ["/usr/libexec/gcc/x86_64-linux-gnu/13/collect2", "-plugin", "/usr/libexec/gcc/x86_64-linux-gnu/13/liblto_plugin.so", "-plugin-opt=/usr/libexec/gcc/x86_64-linux-gnu/13/lto-wrapper", "-plugin-opt=-fresolution=/tmp/ccKbYYb2.res", "-plugin-opt=-pass-through=-lgcc", "-plugin-opt=-pass-through=-lgcc_s", "-plugin-opt=-pass-through=-lc", "-plugin-opt=-pass-through=-lgcc", "-plugin-opt=-pass-through=-lgcc_s", "--build-id", "--eh-frame-hdr", "-m", "elf_x86_64", "--hash-style=gnu", "--as-needed", "-dynamic-linker", "/lib64/ld-linux-x86-64.so.2", "-pie", "-z", "now", "-z", "relro", "-o", "hello", "/usr/lib/gcc/x86_64-linux-gnu/13/../../../x86_64-linux-gnu/Scrt1.o", "/usr/lib/gcc/x86_64-linux-gnu/13/../../../x86_64-linux-gnu/crti.o", "/usr/lib/gcc/x86_64-linux-gnu/13/crtbeginS.o", "-L/usr/lib/gcc/x86_64-linux-gnu/13", "-L/usr/lib/gcc/x86_64-linux-gnu/13/../../../x86_64-linux-gnu", "-L/usr/lib/gcc/x86_64-linux-gnu/13/../../../../lib", "-L/lib/x86_64-linux-gnu", "-L/lib/../lib", "-L/usr/lib/x86_64-linux-gnu", "-L/usr/lib/../lib", "-L/usr/lib/gcc/x86_64-linux-gnu/13/../../..", "/tmp/ccGZrdFz.o", "-lgcc", "--push-state", "--as-needed", "-lgcc_s", "--pop-state", "-lc", "-lgcc", "--push-state", "--as-needed", "-lgcc_s", "--pop-state", "/usr/lib/gcc/x86_64-linux-gnu/13/crtendS.o", "/usr/lib/gcc/x86_64-linux-gnu/13/../../../x86_64-linux-gnu/crtn.o"], 0x7d15df0 /* 72 vars */) = 0
20038 13:48:53 execve("/usr/bin/ld", ["/usr/bin/ld", "-plugin", "/usr/libexec/gcc/x86_64-linux-gnu/13/liblto_plugin.so", "-plugin-opt=/usr/libexec/gcc/x86_64-linux-gnu/13/lto-wrapper", "-plugin-opt=-fresolution=/tmp/ccKbYYb2.res", "-plugin-opt=-pass-through=-lgcc", "-plugin-opt=-pass-through=-lgcc_s", "-plugin-opt=-pass-through=-lc", "-plugin-opt=-pass-through=-lgcc", "-plugin-opt=-pass-through=-lgcc_s", "--build-id", "--eh-frame-hdr", "-m", "elf_x86_64", "--hash-style=gnu", "--as-needed", "-dynamic-linker", "/lib64/ld-linux-x86-64.so.2", "-pie", "-z", "now", "-z", "relro", "-o", "hello", "/usr/lib/gcc/x86_64-linux-gnu/13/../../../x86_64-linux-gnu/Scrt1.o", "/usr/lib/gcc/x86_64-linux-gnu/13/../../../x86_64-linux-gnu/crti.o", "/usr/lib/gcc/x86_64-linux-gnu/13/crtbeginS.o", "-L/usr/lib/gcc/x86_64-linux-gnu/13", "-L/usr/lib/gcc/x86_64-linux-gnu/13/../../../x86_64-linux-gnu", "-L/usr/lib/gcc/x86_64-linux-gnu/13/../../../../lib", "-L/lib/x86_64-linux-gnu", "-L/lib/../lib", "-L/usr/lib/x86_64-linux-gnu", "-L/usr/lib/../lib", "-L/usr/lib/gcc/x86_64-linux-gnu/13/../../..", "/tmp/ccGZrdFz.o", "-lgcc", "--push-state", "--as-needed", "-lgcc_s", "--pop-state", "-lc", "-lgcc", "--push-state", "--as-needed", "-lgcc_s", "--pop-state", "/usr/lib/gcc/x86_64-linux-gnu/13/crtendS.o", "/usr/lib/gcc/x86_64-linux-gnu/13/../../../x86_64-linux-gnu/crtn.o"], 0x7ffd0bf6c850 /* 72 vars */) = 0
20038 13:48:54 +++ exited with 0 +++
20037 13:48:54 --- SIGCHLD {si_signo=SIGCHLD, si_code=CLD_EXITED, si_pid=20038, si_uid=1000, si_status=0, si_utime=4 /* 0.04 s */, si_stime=23 /* 0.23 s */} ---
20037 13:48:54 +++ exited with 0 +++
20029 13:48:54 --- SIGCHLD {si_signo=SIGCHLD, si_code=CLD_EXITED, si_pid=20037, si_uid=1000, si_status=0, si_utime=0, si_stime=3 /* 0.03 s */} ---
20029 13:48:54 +++ exited with 0 +++

编译流程分析

Initial GCC Invocation

execve("/usr/bin/gcc", ["gcc", "-o", "hello", "hello.c"], ...)

Process ID: 20029
Action: Invokes the GCC driver (/usr/bin/gcc).

Compilation Phase

execve("/usr/libexec/gcc/x86_64-linux-gnu/13/cc1", ["/usr/libexec/gcc/x86_64-linux-gnu/13/cc1", ...], ...)

Process ID: 20034
Role:
- cc1 is the GCC C compiler frontend.
- Converts hello.c to assembly code (/tmp/ccLfEVyN.s).
Flags Passed:
Includes optimization settings (e.g., -mtune=generic, -march=x86-64), security features (-fstack-protector-strong, -Wformat-security), and others.

Result:
Assembly file generated at /tmp/ccLfEVyN.s.

Assembly Phase

Attempts to locate the assembler (as):

execve("/usr/local/sbin/as", ...) = -1 ENOENT
execve("/usr/local/bin/as", ...) = -1 ENOENT
execve("/usr/sbin/as", ...) = -1 ENOENT
execve("/usr/bin/as", ...) = 0

Process ID: 20036
Why Multiple Tries?:
GCC searches standard paths for the assembler. Succeeds with /usr/bin/as (GNU Assembler).
Action:
Assembles /tmp/ccLfEVyN.s into an object file: /tmp/ccGZrdFz.o.

Linking Phase

execve("/usr/libexec/gcc/x86_64-linux-gnu/13/collect2", [...], ...)

Process ID: 20037
Role:
- Wrapper for the linker (ld).
- Prepares metadata for C++ static constructors/destructors (not needed here since hello.c is plain C).
- Invokes the real linker (/usr/bin/ld).

Internal Linker Call:

execve("/usr/bin/ld", [...], ...)

Process ID: 20038
Key Flags:
- -dynamic-linker /lib64/ld-linux-x86-64.so.2: Sets the dynamic loader.
- -pie: Creates a Position-Independent Executable (security feature).
- -z now and -z relro: Enhance runtime security.
Inputs Linked:
- CRT (C Runtime) files (Scrt1.o, crti.o, crtbeginS.o, crtendS.o, crtn.o).
- Object file: /tmp/ccGZrdFz.o.
- Standard libraries: -lgcc, -lgcc_s, -lc (libc).

Result:
Final executable hello is created.

Success Indicators

All execve() calls return 0 (success).
Processes exit cleanly (+++ exited with 0 +++).
No errors detected in the toolchain path or linking.

Security & Optimization Notes

Stack Protection: Enabled via -fstack-protector-strong.
Hardened Linking:
- -z now: Immediate binding of symbols.
- -z relro: Read-only relocations after relocation.
- -pie: ASLR-friendly executable.
Build ID: Embedded via --build-id for debugging/tracing.

Critical Paths

Tool	Path	Purpose
`cc1`	`/usr/libexec/gcc/x86_64-linux-gnu/13/cc1`	Compiles C to assembly
`as`	`/usr/bin/as`	Assembles `.s` to `.o`
`collect2`	`/usr/libexec/gcc/x86_64-linux-gnu/13/collect2`	Manages linker setup
`ld`	`/usr/bin/ld`	Links objects into final binary

Conclusion

The log confirms a standard GCC compilation pipeline:

Preprocessing + Parsing: Handled by cc1.
Assembly: Done by as.
Linking: Orchestrated by collect2 → ld.

Last updated on May 2, 2025

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