Merge pull request #72031 from ahoppen/ahoppen/lsan-documentation

Improve documentation on how to debug LSAN failures

Author: ahoppen

docs/LSANFailureSymbolication.md

@@ -4,9 +4,9 @@
 
 1. Clone (or pull) swift-docker: https://github.com/apple/swift-docker
 2. Build the Ubuntu 18.04 container: `cd swift-ci/master/ubuntu/18.04; docker build .`
-3. `docker run -it —cpus <CPUs> —memory <Memory> -v ~/<path to your local sources>:/src-on-host:cached —name lsan-reproducer —cap-add=SYS_PTRACE —security-opt seccomp=unconfined <hash that docker build outputs> bash`
+3. `docker run -it --cpus <CPUs> --memory <Memory> -v ~/<path to your local sources>:/src-on-host:cached --name lsan-reproducer --cap-add=SYS_PTRACE --security-opt seccomp=unconfined <hash that docker build outputs> bash`
     - The `-cap-add` and `-security-opt` arguments are needed to run LLDB inside the Docker container
-4. Copy the sources to inside the Docker container: `cp /src-on-host/* ~`
+4. Copy the sources to inside the Docker container: `cp -r /src-on-host/* ~`
     - We need to to this because the build needs a case-sensitive file system and your host machine probably has a case-insensitive file system
 
 Build inside the Container
@@ -36,36 +36,25 @@ Direct leak of 120 byte(s) in 3 object(s) allocated from:
 SUMMARY: LeakSanitizer: 120 byte(s) leaked in 3 allocation(s).
 ```
 2. `lldb -- <your swiftc invocation above>`
-3. Set a breakpoint somewhere in swiftc, eg. at the start of main: `br s -f driver.cpp -l 19`. This should output something like
-
-```
-Breakpoint 1: where = swiftc`main + 4 at driver.cpp:20:10, address = 0x00000000014d25d4
-```
-
-4. Run swiftc to the breakpoint
-5. This should stop you with something like
-
+3. Start running swiftc inside lldb by executing `r`
+4. Find the loaded offset of swift-frontend by running `image list`
+For example, this might output
 ```
-* thread #1, name = 'swiftc', stop reason = breakpoint 1.1
- frame #0: 0x0000555556a265d4 swiftc`main(argc_=168, argv_=0x00007fffffffced8) at driver.cpp:20:10
-  17  #include "swift/DriverTool/DriverTool.h"
-  18   
-  19  int main(int argc_, const char **argv_) {
-→ 20   return swift::mainEntry(argc_, argv_);
-21  }
+[  0] 0AEA10C1 0x0000555555554000 /home/build-user/build/buildbot_incremental_lsan/swift-linux-x86_64/bin/swift-frontend 
+[  1] D52BB67A-BBBB-E429-6E87-FC16144CA7CE-55276DD6 0x00007ffff7ffb000 [vdso] (0x00007ffff7ffb000)
+[  2] 9EA8014C-F020-21A2-9E57-AA3E0512E9BB-6E30541D 0x00007ffff7dd3000 /lib/x86_64-linux-gnu/ld-2.27.so
 ```
-
-6. Find the loaded offset of swift-frontend by subtracting the breakpoint address from the frame address. With the example above, that’s `0x0000555556a265d4 - 0x00000000014d25d4 = 0x555555554000`.
-7. For the frame that you want to symbolicate,, add the offset you computed above to the stack frame in the LSAN report, eg. to symbolicate frame 1 `0x555555554000 + 0x292d81c = 0x555557E8181C`
-8. Look up the address using `image lookup -a <address you computed>`. This should output something like
+The loaded offset is `0x0000555555554000`
+5. For the frame that you want to symbolicate,, add the offset you computed above to the stack frame in the LSAN report, eg. to symbolicate frame 1 `0x555555554000 + 0x292d81c = 0x555557E8181C`
+6. Look up the address using `image lookup -a <address you computed>`. This should output something like
 
 ```
 (lldb) image lookup -a 0x555557E8181C
       Address: swiftc[0x000000000292d81c] (swiftc.PT_LOAD[0]..text + 22056284)
       Summary: swiftc`registerFunctionTest(BridgedStringRef, void*) + 28 at SILBridging.cpp:148:3
 ```
 
-9. Hoorray, you know which function is leaking.
+7. Hoorray, you know which function is leaking.
 
 ### Making Local Changes Inside the Container