dwarf.md

@@ -284,6 +284,45 @@ DWARF information allows `perf` to locate the source code that belongs
 to the "hot" assembler code. Note that the fairly nonsensical `add %al,(%r8)` instructions is info table data, which `perf` is
 interpreting as code.
 
+## lldb
+
+`lldb` can interpret the DWARF data produced by GHC, and in some respects it can do it better than `gdb`.
+
+```wiki
+$ lldb ./fib
+Current executable set to './fib' (x86_64).
+(lldb) break set -f fib.hs -l 3
+Breakpoint 1: where = fib`rnf_info + 207 [inlined] c2rw_entry, address = 0x00000000004056f7
+(lldb) r
+Process 1901610 launched: './fib' (x86_64)
+Process 1901610 stopped
+* thread #1: tid = 1901610, 0x00000000004056f7 fib`rnf_info [inlined] c2rw_entry at fib.hs:3, name = 'fib', stop reason = breakpoint 1.1
+    frame #0: 0x00000000004056f7 fib`rnf_info [inlined] c2rw_entry at fib.hs:3
+   1    fib :: Int -> Int
+   2    fib 0 = 0
+-> 3    fib 1 = 1
+   4    fib n = fib (n-1) + fib (n-2)
+   5    main :: IO ()
+   6    main = print $ sum [ fib i | i <- [3..20]]
+(lldb) image lookup -a 0x00000000004056f7 -v
+      Address: fib[0x00000000004056f7] (fib..text + 10967)
+      Summary: fib`rnf_info + 207 [inlined] c2rw_entry
+               fib`rnf_info + 207 [inlined] c2rr_entry
+               fib`rnf_info + 207 at
+       Module: file = "./fib", arch = "x86_64"
+  CompileUnit: id = {0x00000000}, file = "/data/users/bnitka/tmp/fib.hs", language = "Language(language = 0x0018)"
+     Function: id = {0x000003b1}, name = "fib", range = [0x0000000000405628-0x0000000000405707)
+     FuncType: id = {0x000003b1}, clang_type = "void (void)"
+       Blocks: id = {0x000003b1}, range = [0x00405628-0x00405707)
+               id = {0x00000495}, ranges = [0x00405675-0x0040567f)[0x0040567f-0x00405685)[0x004056e2-0x004056e7)[0x004056d2-0x004056e2)[0x00405685-0x004056c9)[0x004056f7-0x00405707)[0x004056e7-0x004056f7), name = "c2rr_entry"
+               id = {0x00000539}, range = [0x004056f7-0x00405707), name = "c2rw_entry"
+    LineEntry: [0x00000000004056f7-0x0000000000405720): /data/users/bnitka/tmp/fib.hs:3:9
+       Symbol: id = {0x00000057}, range = [0x0000000000405628-0x0000000000405707), name="rnf_info"
+```
+
+
+Note that we get line number + column number, AFAICT there's no way to do that in gdb.
+
 ## Open Issues