[third-party/py-spy/0.3.14] Align virtual address base

Summary:
This fixes a bug where we were calculating incorrect address offsets.

This tool now works on our Python binaries.

Test Plan:
```
$  buck2 run fbsource//third-party/py-spy/0.3.14:py-spy -- dump -p 1245593
```

Reviewers: bmaurer, itamaro, lisroach

Reviewed By: bmaurer

Subscribers: mzlee

Differential Revision: https://phabricator.intern.facebook.com/D50649635

Cargo.toml

@@ -31,6 +31,7 @@ lru = "0.10"
 num-traits = "0.2"
 regex = ">=1.6.0"
 tempfile = "3.6.0"
+page_size = "0.6.0"
 proc-maps = "0.4.0"
 memmap2 = "0.9.4"
 cpp_demangle = "0.4"

src/binary_parser.rs

@@ -150,9 +150,11 @@ pub fn parse_binary(filename: &Path, addr: u64, size: u64) -> Result<BinaryInfo,
                     )
                 })?;
 
-            // p_vaddr may be larger than the map address in case when the header has an offset and
-            // the map address is relatively small. In this case we can default to 0.
-            let offset = offset.saturating_sub(program_header.p_vaddr);
+            // Align the virtual address offset, then subtract it from the offset
+            // to get real offset for symbol addresses in the file.
+            let aligned_vaddr =
+                program_header.p_vaddr - (program_header.p_vaddr % page_size::get() as u64);
+            let offset = offset - aligned_vaddr;
 
             let mut bss_addr = 0;
             let mut bss_size = 0;