Messages in this thread | | | From | (Kanoj Sarcar) | Subject | dso loading question | Date | Wed, 26 May 1999 21:44:41 -0700 (PDT) |
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I am trying to understand how the glibc ld-linux code works just after program startup. I have a small program
main() { }
on which I ran strace to get the following output:
[kanoj@entity /tmp]$ strace ./a.out execve("./a.out", ["./a.out"], [/* 18 vars */]) = 0 brk(0) = 0x8049558 open("/etc/ld.so.preload", O_RDONLY) = -1 ENOENT (No such file or directory) open("/etc/ld.so.cache", O_RDONLY) = 3 fstat(3, {st_mode=0, st_size=0, ...}) = 0 mmap(0, 11908, PROT_READ, MAP_PRIVATE, 3, 0) = 0x4000b000 close(3) = 0 open("/lib/libc.so.6", O_RDONLY) = 3 mmap(0, 4096, PROT_READ, MAP_PRIVATE, 3, 0) = 0x4000e000 munmap(0x4000e000, 4096) = 0 mmap(0, 670420, PROT_READ|PROT_EXEC, MAP_PRIVATE, 3, 0) = 0x4000e000 mprotect(0x4009f000, 76500, PROT_NONE) = 0 mmap(0x4009f000, 28672, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED, 3, 0x90000) = 0x4009f000 mmap(0x400a6000, 47828, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = 0x400a6000 close(3) = 0 personality(PER_LINUX) = 0 getpid() = 9822 _exit(134513792) = ?
Here are the questions I would like to get answers to: 1. What is the purpose of the /etc/ld.so.cache? Where can I learn more about it? 2. I assume the first 4K mmap of libc is to read section headers etc ... or is there something more going on there? 3. How are the libc mmap/munmap calls made by the loading code? Basically, how does the code decide on the offset/length to mmap? Why is an mprotect being done? 4. Are the .init sections of the dso's executed before the close() of the fd referencing the dso? 5. At what point is the personality(PER_LINUX) call made?
I am trying to understand how dso loading works in Linux, specially at program startup time.
Thanks for any input. Please CC me on any responses at kanoj@engr.sgi.com.
Kanoj kanoj@engr.sgi.com
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