feat(elfunwindinfo): add LookupFDE #545
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,144 @@ | ||
| // Copyright The OpenTelemetry Authors | ||
| // SPDX-License-Identifier: Apache-2.0 | ||
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| package elfunwindinfo // import "go.opentelemetry.io/ebpf-profiler/nativeunwind/elfunwindinfo" | ||
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| import ( | ||
| "debug/elf" | ||
| "errors" | ||
| "fmt" | ||
| "sort" | ||
| "unsafe" | ||
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| lru "github.com/elastic/go-freelru" | ||
| "go.opentelemetry.io/ebpf-profiler/libpf" | ||
| "go.opentelemetry.io/ebpf-profiler/libpf/pfelf" | ||
| ) | ||
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| type FDE struct { | ||
| PCBegin uintptr | ||
| PCRange uintptr | ||
| } | ||
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| type EhFrameTable struct { | ||
| r reader | ||
| hdr *ehFrameHdr | ||
| fdeCount uintptr | ||
| tableStartPos uintptr | ||
| ehFrameSec *elfRegion | ||
| efm elf.Machine | ||
| cieCache *lru.LRU[uint64, *cieInfo] | ||
| } | ||
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| // NewEhFrameTable creates a new EhFrameTable from the given pfelf.File | ||
| // The returned EhFrameTable must not be used concurrently | ||
| func NewEhFrameTable(ef *pfelf.File) (*EhFrameTable, error) { | ||
| ehFrameHdrSec, ehFrameSec, err := findEhSections(ef) | ||
| if err != nil { | ||
| return nil, fmt.Errorf("failed to get EH sections: %w", err) | ||
| } | ||
| if ehFrameSec == nil { | ||
| return nil, errors.New(".eh_frame not found") | ||
| } | ||
| if ehFrameHdrSec == nil { | ||
| return nil, errors.New(".eh_frame_hdr not found") | ||
| } | ||
| return newEhFrameTableFromSections(ehFrameHdrSec, ehFrameSec, ef.Machine) | ||
| } | ||
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| // LookupFDE performs a binary search in .eh_frame_hdr for an FDE covering the given addr. | ||
| func (e *EhFrameTable) LookupFDE(addr libpf.Address) (FDE, error) { | ||
| idx := sort.Search(e.count(), func(idx int) bool { | ||
| e.position(idx) | ||
| ipStart, _, _ := e.parseHdrEntry() // ignoring error, check bounds later | ||
| return ipStart > uintptr(addr) | ||
| }) | ||
| if idx <= 0 { | ||
| return FDE{}, errors.New("FDE not found") | ||
| } | ||
| e.position(idx - 1) | ||
| ipStart, fr, entryErr := e.parseHdrEntry() | ||
| if entryErr != nil { | ||
| return FDE{}, entryErr | ||
| } | ||
| _, fde, _, err := parsesFDEHeader(&fr, e.efm, ipStart, e.cieCache) | ||
| if err != nil { | ||
| return FDE{}, err | ||
| } | ||
| if uintptr(addr) < fde.ipStart || uintptr(addr) >= fde.ipStart+fde.ipLen { | ||
| return FDE{}, errors.New("FDE not found") | ||
| } | ||
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| return FDE{ | ||
| PCBegin: fde.ipStart, | ||
| PCRange: fde.ipLen, | ||
| }, nil | ||
| } | ||
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| func newEhFrameTableFromSections(ehFrameHdrSec *elfRegion, | ||
| ehFrameSec *elfRegion, efm elf.Machine, | ||
| ) (hp *EhFrameTable, err error) { | ||
| hp = &EhFrameTable{ | ||
| hdr: (*ehFrameHdr)(unsafe.Pointer(&ehFrameHdrSec.data[0])), | ||
| r: ehFrameHdrSec.reader(unsafe.Sizeof(ehFrameHdr{}), false), | ||
| } | ||
| if _, err = hp.r.ptr(hp.hdr.ehFramePtrEnc); err != nil { | ||
| return hp, err | ||
| } | ||
| if hp.fdeCount, err = hp.r.ptr(hp.hdr.fdeCountEnc); err != nil { | ||
| return hp, err | ||
| } | ||
| if hp.cieCache, err = lru.New[uint64, *cieInfo](cieCacheSize, hashUint64); err != nil { | ||
| return hp, err | ||
| } | ||
| hp.ehFrameSec = ehFrameSec | ||
| hp.tableStartPos = hp.r.pos | ||
| hp.efm = efm | ||
| return hp, nil | ||
| } | ||
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| // returns FDE count | ||
| func (e *EhFrameTable) count() int { | ||
| return int(e.fdeCount) | ||
| } | ||
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| // position adjusts the reader position to point at the table entry with idx index | ||
| func (e *EhFrameTable) position(idx int) { | ||
| tableEntrySize := formatLen(e.hdr.tableEnc) * 2 | ||
| e.r.pos = e.tableStartPos + uintptr(tableEntrySize*idx) | ||
| } | ||
|
Comment on lines
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+109
Contributor
There was a problem hiding this comment. last minute nit: this makes |
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| // parseHdrEntry parsers an entry in the .eh_frame_hdr binary search table and the corresponding | ||
| // entry in the .eh_frame section | ||
| func (e *EhFrameTable) parseHdrEntry() (ipStart uintptr, fr reader, err error) { | ||
| ipStart, err = e.r.ptr(e.hdr.tableEnc) | ||
| if err != nil { | ||
| return 0, reader{}, err | ||
| } | ||
| var fdeAddr uintptr | ||
| fdeAddr, err = e.r.ptr(e.hdr.tableEnc) | ||
| if err != nil { | ||
| return 0, reader{}, err | ||
| } | ||
| if fdeAddr < e.ehFrameSec.vaddr { | ||
| return 0, reader{}, fmt.Errorf("FDE %#x before section start %#x", | ||
| fdeAddr, e.ehFrameSec.vaddr) | ||
| } | ||
| fr = e.ehFrameSec.reader(fdeAddr-e.ehFrameSec.vaddr, false) | ||
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| return ipStart, fr, err | ||
| } | ||
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| // formatLen returns the length of a field encoded with enc encoding. | ||
| func formatLen(enc encoding) int { | ||
| switch enc & encFormatMask { | ||
| case encFormatData2: | ||
| return 2 | ||
| case encFormatData4: | ||
| return 4 | ||
| case encFormatData8, encFormatNative: | ||
| return 8 | ||
| default: | ||
| return 0 | ||
| } | ||
| } | ||
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