Update build advice for benchmarking and profiling

[delan]

These patches update the Profiling and Building Servo chapters with new advice around building Servo for benchmarking and profiling purposes. In particular:

• we document the new production-stripped (Add production-stripped cargo profile servo#32651) and profiling (Add a profiling build profile in Cargo servo#33432) profiles
• we recommend using profiling builds for profiling, rather than release builds with debug info and thin local LTO
• we clarify that production builds are more optimised than release builds, and they still have symbols

We also fix a typo, --with-frame-pointers → --with-frame-pointer. That said, we should really enable stack frame pointers by default in all builds, because it’s now considered best practice.

(@atbrakhi, @jschwe)

[jschwe]

That said, we should really enable stack frame pointers by default in all builds, because it’s now considered best practice.

Yes, please! Although perhaps the default is already "On" for rust code (rust-lang/rust#122646 (comment)). I didn't check yet what the defaults for framepointers in user code are on the targets we support.

[delan]

Yes, please! Although perhaps the default is already "On" for rust code (rust-lang/rust#122646 (comment)). I didn't check yet what the defaults for framepointers in user code are on the targets we support.

Regarding user code, it seems they are not yet forced by default on all platforms. I checked this by finding related patches (rust-lang/rust#61675, rust-lang/rust#86652, rust-lang/rust#107689, rust-lang/rust#114323, rust-lang/rust#115521, rust-lang/rust#124733) and seeing where the defaults are specified:

~/code/rust $ git log -n 1 --pretty=oneline
702987f75b74f789ba227ee04a3d7bb1680c2309 (HEAD -> master, origin/master, origin/HEAD) Auto merge of #130732 - matthiaskrgr:rollup-ke1j314, r=matthiaskrgr

~/code/rust $ rg frame_pointer: compiler/rustc_target/src/spec/mod.rs
2169:    pub frame_pointer: FramePointer,
2564:            frame_pointer: FramePointer::MayOmit,

~/code/rust $ rg --sort=path frame_pointer compiler/rustc_target/src/spec/targets | cat
compiler/rustc_target/src/spec/targets/aarch64_apple_darwin.rs:            frame_pointer: FramePointer::NonLeaf,
compiler/rustc_target/src/spec/targets/aarch64_apple_ios.rs:            frame_pointer: FramePointer::NonLeaf,
compiler/rustc_target/src/spec/targets/aarch64_apple_ios_macabi.rs:            frame_pointer: FramePointer::NonLeaf,
compiler/rustc_target/src/spec/targets/aarch64_apple_ios_sim.rs:            frame_pointer: FramePointer::NonLeaf,
compiler/rustc_target/src/spec/targets/aarch64_apple_tvos.rs:            frame_pointer: FramePointer::NonLeaf,
compiler/rustc_target/src/spec/targets/aarch64_apple_tvos_sim.rs:            frame_pointer: FramePointer::NonLeaf,
compiler/rustc_target/src/spec/targets/aarch64_apple_visionos.rs:            frame_pointer: FramePointer::NonLeaf,
compiler/rustc_target/src/spec/targets/aarch64_apple_visionos_sim.rs:            frame_pointer: FramePointer::NonLeaf,
compiler/rustc_target/src/spec/targets/aarch64_apple_watchos_sim.rs:            frame_pointer: FramePointer::NonLeaf,
compiler/rustc_target/src/spec/targets/arm64e_apple_darwin.rs:            frame_pointer: FramePointer::NonLeaf,
compiler/rustc_target/src/spec/targets/arm64e_apple_ios.rs:            frame_pointer: FramePointer::NonLeaf,
compiler/rustc_target/src/spec/targets/arm64e_apple_tvos.rs:            frame_pointer: FramePointer::NonLeaf,
compiler/rustc_target/src/spec/targets/armv5te_none_eabi.rs:            frame_pointer: FramePointer::MayOmit,
compiler/rustc_target/src/spec/targets/i686_apple_darwin.rs:            frame_pointer: FramePointer::Always,
compiler/rustc_target/src/spec/targets/i686_pc_windows_gnu.rs:    base.frame_pointer = FramePointer::Always; // Required for backtraces
compiler/rustc_target/src/spec/targets/i686_pc_windows_gnullvm.rs:    base.frame_pointer = FramePointer::Always; // Required for backtraces
compiler/rustc_target/src/spec/targets/i686_unknown_linux_musl.rs:    base.frame_pointer = FramePointer::Always;
compiler/rustc_target/src/spec/targets/i686_uwp_windows_gnu.rs:    base.frame_pointer = FramePointer::Always; // Required for backtraces
compiler/rustc_target/src/spec/targets/thumbv4t_none_eabi.rs:            frame_pointer: FramePointer::MayOmit,
compiler/rustc_target/src/spec/targets/thumbv5te_none_eabi.rs:            frame_pointer: FramePointer::MayOmit,
compiler/rustc_target/src/spec/targets/x86_64_apple_darwin.rs:            frame_pointer: FramePointer::Always,
compiler/rustc_target/src/spec/targets/x86_64h_apple_darwin.rs:    opts.frame_pointer = FramePointer::Always;

I also confirmed this in our own builds for Linux on amd64. Most functions have frame pointers, but not all:

~/code/servo $ git log -n 1 --pretty=oneline
d3d6a22d27df5095c3342249d0eea0bce153cbe1 (HEAD -> main, upstream/main) ohos: Add back and fwd button to vendored app (#33511)

~/code/servo $ ./mach build --profile profiling
~/code/servo $ objdump -dSM intel target/profiling/servo | pv > objdump_profiling.txt
~/code/servo $ fgrep -A9 '_ZN67_$LT$layout_2020..dom..BoxSlot$u20$as$u20$core..ops..drop..Drop$GT$4drop17h03488a18e530c6c8E' objdump_profiling.txt
0000000000cf8e90 <_ZN67_$LT$layout_2020..dom..BoxSlot$u20$as$u20$core..ops..drop..Drop$GT$4drop17h03488a18e530c6c8E>:
}

impl Drop for BoxSlot<'_> {
    fn drop(&mut self) {
  cf8e90:	53                   	push   rbx
  cf8e91:	48 83 ec 50          	sub    rsp,0x50
  cf8e95:	48 8d 05 2c 2e c2 05 	lea    rax,[rip+0x5c22e2c]        # 691bcc8 <_ZN3std9panicking11panic_count18GLOBAL_PANIC_COUNT17hd7fda31a6dd5a9d3E>
  cf8e9c:	48 8b 00             	mov    rax,QWORD PTR [rax]
  cf8e9f:	48 d1 e0             	shl    rax,1

~/code/servo $ ./mach build --profile profiling --with-frame-pointer
~/code/servo $ objdump -dSM intel target/profiling/servo | pv > objdump_profiling_wfp.txt
~/code/servo $ fgrep -A9 '_ZN67_$LT$layout_2020..dom..BoxSlot$u20$as$u20$core..ops..drop..Drop$GT$4drop17h03488a18e530c6c8E' objdump_profiling_wfp.txt
0000000000cf03d0 <_ZN67_$LT$layout_2020..dom..BoxSlot$u20$as$u20$core..ops..drop..Drop$GT$4drop17h03488a18e530c6c8E>:
}

impl Drop for BoxSlot<'_> {
    fn drop(&mut self) {
  cf03d0:	55                   	push   rbp
  cf03d1:	48 89 e5             	mov    rbp,rsp
  cf03d4:	53                   	push   rbx
  cf03d5:	48 83 ec 58          	sub    rsp,0x58
  cf03d9:	48 8d 05 e8 88 b4 05 	lea    rax,[rip+0x5b488e8]        # 6838cc8 <_ZN3std9panicking11panic_count18GLOBAL_PANIC_COUNT17hd7fda31a6dd5a9d3E>