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Exception::CallStack: avoid allocations in LibC.dl_iterate_phdr #12625

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Nov 12, 2022
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Exception::CallStack: avoid allocations in LibC.dl_iterate_phdr #12625

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15 changes: 9 additions & 6 deletions src/exception/call_stack/elf.cr
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Original file line number Diff line number Diff line change
Expand Up @@ -5,16 +5,19 @@ require "crystal/elf"

struct Exception::CallStack
protected def self.load_debug_info_impl
base_address : LibC::Elf_Addr = 0
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I would avoid using a TypeDeclaration here unless necessary:

Suggested change
base_address : LibC::Elf_Addr = 0
base_address = LibC::Elf_Addr.zero

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Later we're passing a pointer to this variable. So IMO it makes sense to pin its type in order to prevent an accidental union type tainting the pointer.

phdr_callback = LibC::DlPhdrCallback.new do |info, size, data|
# The first entry is the header for the current program
read_dwarf_sections(info.value.addr)
# The first entry is the header for the current program.
# Note that we avoid allocating here and just store the base address
# to be passed to self.read_dwarf_sections when dl_iterate_phdr returns.
# Calling self.read_dwarf_sections from this callback may lead to reallocations
# and deadlocks due to the internal lock held by dl_iterate_phdr (#10084).
data.as(Pointer(LibC::Elf_Addr)).value = info.value.addr
1
end

# GC needs to be disabled around dl_iterate_phdr in freebsd (#10084)
{% if flag?(:freebsd) %} GC.disable {% end %}
LibC.dl_iterate_phdr(phdr_callback, nil)
{% if flag?(:freebsd) %} GC.enable {% end %}
LibC.dl_iterate_phdr(phdr_callback, pointerof(base_address))
self.read_dwarf_sections(base_address)
end

protected def self.read_dwarf_sections(base_address = 0)
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