cargo: build with frame pointers (#10226)

## Problem

Frame pointers are typically disabled by default (depending on CPU
architecture), to improve performance. This frees up a CPU register, and
avoids a couple of instructions per function call. However, it makes
stack unwinding much more inefficient, since it has to use DWARF debug
information instead, and gives worse results with e.g. `perf` and eBPF
profiles. The `backtrace` implementation of `libunwind` is also
suspected to cause seg faults.

The performance benefit of frame pointer omission doesn't appear to
matter that much on modern 64-bit CPU architectures (which have plenty
of registers and optimized instruction execution), and benchmarks did
not show measurable overhead.

The Rust standard library and jemalloc already enable frame pointers by
default.

For more information, see
https://www.brendangregg.com/blog/2024-03-17/the-return-of-the-frame-pointers.html.

Resolves #10224.
Touches #10225.

## Summary of changes

Enable frame pointers in all builds, and use frame pointers for pprof-rs
stack sampling.

.cargo/config.toml

@@ -3,6 +3,14 @@
 # by the RUSTDOCFLAGS env var in CI.
 rustdocflags = ["-Arustdoc::private_intra_doc_links"]
 
+# Enable frame pointers. This may have a minor performance overhead, but makes it easier and more
+# efficient to obtain stack traces (and thus CPU/heap profiles). With continuous profiling, this is
+# likely a net win, and allows higher profiling resolution. See also:
+#
+# * <https://www.brendangregg.com/blog/2024-03-17/the-return-of-the-frame-pointers.html>
+# * <https://github.com/rust-lang/rust/pull/122646>
+rustflags = ["-Cforce-frame-pointers=yes"]
+
 [alias]
 build_testing = ["build", "--features", "testing"]
 neon = ["run", "--bin", "neon_local"]

Cargo.toml

@@ -135,7 +135,7 @@ parquet = { version = "53", default-features = false, features = ["zstd"] }
 parquet_derive = "53"
 pbkdf2 = { version = "0.12.1", features = ["simple", "std"] }
 pin-project-lite = "0.2"
-pprof = { version = "0.14", features = ["criterion", "flamegraph", "protobuf", "protobuf-codec"] }
+pprof = { version = "0.14", features = ["criterion", "flamegraph", "frame-pointer", "protobuf", "protobuf-codec"] }
 procfs = "0.16"
 prometheus = {version = "0.13", default-features=false, features = ["process"]} # removes protobuf dependency
 prost = "0.13"
@@ -266,6 +266,8 @@ tokio-postgres = { git = "https://github.com/neondatabase/rust-postgres.git", br
 [profile.release]
 # This is useful for profiling and, to some extent, debug.
 # Besides, debug info should not affect the performance.
+#
+# NB: we also enable frame pointers for improved profiling, see .cargo/config.toml.
 debug = true
 
 # disable debug symbols for all packages except this one to decrease binaries size