…em with duff routines This patch provides a fix for a problem linking large arm32 binaries with external linking, specifically R_CALLARM relocations against runtime.duff* routines being flagged by the external linker as not reaching. What appears to be happening in the bug in question is that the Go linker and the external linker are using slightly different recipes to decide whether a given R_CALLARM relocation will "fit" (e.g. will not require a trampoline). The Go linker is taking into account the addend on the call reloc (which for calls to runtime.duffcopy or runtime.duffzero is nonzero), whereas the external linker appears to be ignoring the addend. Example to illustrate: Addr Size Func ----- ----- ----- ... XYZ 1024 runtime.duffcopy ... ABC ... mypackge.MyFunc + R0: R_CALLARM o=8 a=848 tgt=runtime.duffcopy<0> Let's say that the distance between ABC (start address of runtime.duffcopy) and XYZ (start of MyFunc) is just over the architected 24-bit maximum displacement for an R_CALLARM (let's say that ABC-XYZ is just over the architected limit by some small value, say 36). Because we're calling into runtime.duffcopy at offset 848, however, the relocation does in fact fit, but if the external linker isn't taking into account the addend (assuming that all calls target the first instruction of the called routine), then we'll get a "doesn't fit" error from the linker. To work around this problem, revise the ARM trampoline generation code in the Go linker that computes the trampoline threshold to ignore the addend on R_CALLARM relocations, so as to harmonize the two linkers. Fixes #58503. Updates #58428. Updates #58425. Change-Id: I56e580c05b7b47bbe8edf5532a1770bbd700fbe5 Reviewed-on: https://go-review.googlesource.com/c/go/+/469275 TryBot-Result: Gopher Robot <gobot@golang.org> Reviewed-by: Cherry Mui <cherryyz@google.com> Run-TryBot: Than McIntosh <thanm@google.com> (cherry picked from commit 0b5affb) Reviewed-on: https://go-review.googlesource.com/c/go/+/471597

cmd/link: relocation truncated to fit: R_ARM_CALL against `runtime.duffcopy' [1.20 backport] #58503

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