migrated runtime-ld.txt

1 files changed, 0 insertions, 115 deletions

diff --git a/runtime-ld.txt b/runtime-ld.txt
deleted file mode 100644
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--- a/runtime-ld.txt
+++ /dev/null
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-# runtime ld
---------------------------------------------------------------------------------
-
-# toc
-------
-  |ld_so|
-    |load_init_order|
-    |dynamic_linking|
-
-# ld.so(8)                                                               *ld_so*
-===========
-  env:
-    LD_PRELOAD=<l_so>       colon separated list of libso's to be pre loaded
-    LD_DEBUG=<opts>         comman separated list of debug options
-            =help           list available options
-            =libs           show library search path
-            =files          processing of input files
-            =symbols        show search path for symbol lookup
-            =bindings       show against which definition a symbol is bound
-
-
-  ## LD_PRELOAD load & init order                              *load_init_order*
-    > ldd ./main
-      >> libc.so.6 => /usr/lib/libc.so.6
-
-    > LD_PRELOAD=liba.so:libb.so ./main
-               -->
-        preloaded in this order
-               <--
-        initialized in this order
-
-    - preload order determines the order libs are inserted into the link map
-
-    - resulting link map:
-        +------+    +------+    +------+    +------+
-        | main | -> | liba | -> | libb | -> | libc |
-        +------+    +------+    +------+    +------+
-
-    - see preload and init order in action
-      > LD_DEBUG=files LD_PRELOAD=liba.so:libb.so ./main
-        # load order (-> determines link map)
-        >> file=liba.so [0];  generating link map
-        >> file=libb.so [0];  generating link map
-        >> file=libc.so.6 [0];  generating link map
-
-        # init order
-        >> calling init: /usr/lib/libc.so.6
-        >> calling init: <path>/libb.so
-        >> calling init: <path>/liba.so
-        >> initialize program: ./main
-
-    - see the symbol lookup in action and therefore the link map order
-      > LD_DEBUG=symbols,bindings LD_PRELOAD=liba.so:libb.so ./main
-        >> symbol=memcpy;  lookup in file=./main [0]
-        >> symbol=memcpy;  lookup in file=<path>/liba.so [0]
-        >> symbol=memcpy;  lookup in file=<path>/libb.so [0]
-        >> symbol=memcpy;  lookup in file=/usr/lib/libc.so.6 [0]
-        >> binding file ./main [0] to /usr/lib/libc.so.6 [0]: normal symbol
-           `memcpy' [GLIBC_2.14]
-
-  ## dynamic linking (x86_64)                                  *dynamic_linking*
-    - dynamic linking basically works via one indirect jump. It uses a
-      combination of function trampolines (.plt) and a function pointer table
-      (.got.plt). On the first call the trampoline sets up some metadata and
-      then jumps to the ld.so runtime resolve function, which in turn patches
-      the table with the correct function pointer.
-        .plt ....... contains function trampolines, usually located in code
-                     segment (rx permission)
-        .got.plt ... hold the function pointer table
-
-    - following r2 dump shows this
-        - [0x00401030] indirect jump for 'puts' using function pointer in
-          _GLOBAL_OFFSET_TABLE_[3]
-        - initially points to instruction behind 'puts' trampoline [0x00401036]
-        - this pushes relocation index and then jumps to the first trampoline
-          [0x00401020]
-        - the first trampoline jumps to _GLOBAL_OFFSET_TABLE_[2] which will be
-          filled at program startup by the ld.so with its resolve function
-        - the resolve function fixes the relocation referenced by the
-          relocation index pushed by the 'puts' trampoline
-        - the relocation entry tells the resolve function which symbol to
-          search for and where to put the function pointer
-            > readelf -r <main>
-              >> Relocation section '.rela.plt' at offset 0x4b8 contains 1 entry:
-              >>   Offset          Info           Type           Sym. Value    Sym. Name + Addend
-              >> 000000404018  000200000007 R_X86_64_JUMP_SLO 0000000000000000 puts@GLIBC_2.2.5 + 0
-            - offset points to _GLOBAL_OFFSET_TABLE_[3]
-
-        [0x00401040]> pd 4 @ section..got.plt
-                    ;-- section..got.plt:
-                    ;-- .got.plt:    ; [22] -rw- section size 32 named .got.plt
-                    ;-- _GLOBAL_OFFSET_TABLE_:
-                    0x00404000      .qword 0x0000000000403e10 ; section..dynamic ; obj._DYNAMIC
-                    0x00404008      .qword 0x0000000000000000
-                    ; CODE XREF from section..plt @ +0x6
-                    0x00404010      .qword 0x0000000000000000
-                    ;-- reloc.puts:
-                    ; CODE XREF from sym.imp.puts @ 0x401030
-                    0x00404018      .qword 0x0000000000401036                  ; RELOC 64 puts
-
-        [0x00401040]> pd 6 @ section..plt
-                    ;-- section..plt:
-                    ;-- .plt:       ; [12] -r-x section size 32 named .plt
-                ┌─> 0x00401020      ff35e22f0000   push qword [0x00404008]
-                ╎   0x00401026      ff25e42f0000   jmp qword [0x00404010]
-                ╎   0x0040102c      0f1f4000       nop dword [rax]
-        ┌ 6: int sym.imp.puts (const char *s);
-        └       ╎   0x00401030      ff25e22f0000   jmp qword [reloc.puts]
-                ╎   0x00401036      6800000000     push 0
-                └─< 0x0040103b      e9e0ffffff     jmp sym..plt
-
-
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-vim:ft=help:sts=2:et:tw=80:cc=80:fo+=t
-