Hi Marcus, applied and pushed, after intensive testing with Qemu and uClibc-ng-test.
thanks Waldemar Marcus Hähnel wrote, > ... and here is the attachment ... > > > > > On Thu, 2025-03-20 at 09:39 +0100, Marcus Hähnel wrote: > > Dear List > > > > So far, uclibc relied on the informal behaviour of GNU ld to put the link > > address of the _DYNAMIC symbol in the first GOT > > entry. This does not work with LLVM lld which does not follow this > > convention. Consequently, glibc has abandoned its usage > > in favour of using __ehdr_start as magic symbol to infer the load address > > [1]. > > > > Note that this implies that the link time address of __ehdr_start is > > *always* 0! So far, this seems to be the case on all > > platforms. > > > > We implemented this change only for the platforms which we actively support > > and test at Kernkonzept (arm64, arm, i386, > > x86_64 and and riscv). The riscv64 dl-sysdep.h already used the method we > > converted the others to. For the other platforms > > we do not have the capacity to port this, but as long as noone wants to > > build them using lld this should not be an issue. > > > > Please feel free to test this on the relevant platforms before merging, to > > be sure it works as intended with the upstream > > version of the lib. > > > > Best regards, > > > > - Marcus > > > > > > [1] https://sourceware.org/bugzilla/show_bug.cgi?id=28203 > > > > > > > > > > -- > +++++++++++++++++++ > > > Register now for our workshop "Get to know L4Re in 3 days" on April 8-10. > Learn to design and deploy secure system > architectures for your product with L4Re: > https://www.kernkonzept.com/workshop-getting-started-with-l4re/ > > +++++++++++++++++++ > > Kernkonzept GmbH > Sitz: Dresden > HRB 31129 > Geschäftsführer: Dr.-Ing. Michael Hohmuth > > > From 9a4929ce522d34bed13c24e88c58ae48f1c538c5 Mon Sep 17 00:00:00 2001 > From: =?UTF-8?q?Jan=20Kl=C3=B6tzke?= <jan.kloet...@kernkonzept.com> > Date: Tue, 18 Mar 2025 07:41:47 +0100 > Subject: [PATCH] Use __ehdr_start to compute load address > > So far, uclibc relied on the informal behaviour of GNU ld to put the > link address of the _DYNAMIC symbol in the first GOT entry. This does > not work with LLVM lld which does not follow this convention. > Consequently, glibc has abandoned its usage in favour of using > __ehdr_start as magic symbol to infer the load address [1]. > > Note that this implies that the link time address of __ehdr_start is > *always* 0! So far, this seems to be the case on all platforms. > > [1] https://sourceware.org/bugzilla/show_bug.cgi?id=28203 > > Signed-off-by: Marcus Haehnel <marcus.haeh...@kernkonzept.com> > --- > ldso/ldso/aarch64/dl-sysdep.h | 25 +++++-------- > ldso/ldso/arm/dl-sysdep.h | 69 +++++------------------------------ > ldso/ldso/i386/dl-sysdep.h | 27 +++++--------- > ldso/ldso/riscv32/dl-sysdep.h | 22 +++++------ > ldso/ldso/x86_64/dl-sysdep.h | 45 +++++------------------ > 5 files changed, 48 insertions(+), 140 deletions(-) > > diff --git a/ldso/ldso/aarch64/dl-sysdep.h b/ldso/ldso/aarch64/dl-sysdep.h > index 6d9d2c1fb..3466920d9 100644 > --- a/ldso/ldso/aarch64/dl-sysdep.h > +++ b/ldso/ldso/aarch64/dl-sysdep.h > @@ -54,28 +54,21 @@ unsigned long _dl_linux_resolver(struct elf_resolve * > tpnt, int reloc_entry); > || (type) == R_AARCH64_TLSDESC) * ELF_RTYPE_CLASS_PLT) \ > | (((type) == R_AARCH64_COPY) * ELF_RTYPE_CLASS_COPY)) > > -/* Return the link-time address of _DYNAMIC. Conveniently, this is the > - first element of the GOT. */ > -extern const ElfW(Addr) _GLOBAL_OFFSET_TABLE_[] attribute_hidden; > -static __always_inline ElfW(Addr) __attribute__ ((unused)) > -elf_machine_dynamic (void) > -{ > - return _GLOBAL_OFFSET_TABLE_[0]; > -} > - > /* Return the run-time load address of the shared object. */ > > static __always_inline ElfW(Addr) __attribute__ ((unused)) > elf_machine_load_address (void) > { > - /* To figure out the load address we use the definition that for any > symbol: > - dynamic_addr(symbol) = static_addr(symbol) + load_addr > - > - _DYNAMIC sysmbol is used here as its link-time address stored in > - the special unrelocated first GOT entry. */ > + extern const ElfW(Ehdr) __ehdr_start attribute_hidden; > + return (ElfW(Addr)) &__ehdr_start; > +} > > - extern ElfW(Dyn) _DYNAMIC[] attribute_hidden; > - return (ElfW(Addr)) &_DYNAMIC - elf_machine_dynamic (); > +/* Return the link-time address of _DYNAMIC. */ > +static __always_inline ElfW(Addr) __attribute__ ((unused)) > +elf_machine_dynamic (void) > +{ > + extern ElfW(Dyn) _DYNAMIC[] attribute_hidden; > + return (ElfW(Addr)) _DYNAMIC - elf_machine_load_address (); > } > > static __always_inline void > diff --git a/ldso/ldso/arm/dl-sysdep.h b/ldso/ldso/arm/dl-sysdep.h > index 0f783e1c4..93e36b694 100644 > --- a/ldso/ldso/arm/dl-sysdep.h > +++ b/ldso/ldso/arm/dl-sysdep.h > @@ -96,43 +96,6 @@ unsigned long _dl_linux_resolver(struct elf_resolve * > tpnt, int reloc_entry); > | (((type) == R_ARM_COPY) * ELF_RTYPE_CLASS_COPY)) > #endif /* __FDPIC__ */ > > -/* Return the link-time address of _DYNAMIC. Conveniently, this is the > - first element of the GOT. We used to use the PIC register to do this > - without a constant pool reference, but GCC 4.2 will use a pseudo-register > - for the PIC base, so it may not be in r10. */ > -static __always_inline Elf32_Addr __attribute__ ((unused)) > -elf_machine_dynamic (void) > -{ > - Elf32_Addr dynamic; > -#if !defined __thumb__ > - __asm__ ("ldr %0, 2f\n" > - "1: ldr %0, [pc, %0]\n" > - "b 3f\n" > - "2: .word _GLOBAL_OFFSET_TABLE_ - (1b+8)\n" > - "3:" : "=r" (dynamic)); > -#else > - int tmp; > - __asm__ (".align 2\n" > - "bx pc\n" > - "nop\n" > - ".arm\n" > - "ldr %0, 2f\n" > - "1: ldr %0, [pc, %0]\n" > - "b 3f\n" > - "2: .word _GLOBAL_OFFSET_TABLE_ - (1b+8)\n" > - "3:" > - ".align 2\n" > - "orr %1, pc, #1\n" > - "bx %1\n" > - ".force_thumb\n" > - : "=r" (dynamic), "=&r" (tmp)); > -#endif > - > - return dynamic; > -} > - > -extern char __dl_start[] __asm__("_dl_start"); > - > #ifdef __FDPIC__ > /* We must force strings used early in the bootstrap into the data > segment. */ > @@ -148,28 +111,16 @@ extern char __dl_start[] __asm__("_dl_start"); > static __always_inline Elf32_Addr __attribute__ ((unused)) > elf_machine_load_address (void) > { > -#if defined(__FDPIC__) > - return 0; > -#else > - Elf32_Addr got_addr = (Elf32_Addr) &__dl_start; > - Elf32_Addr pcrel_addr; > -#if defined __OPTIMIZE__ && !defined __thumb__ > - __asm__ ("adr %0, _dl_start" : "=r" (pcrel_addr)); > -#else > - /* A simple adr does not work in Thumb mode because the offset is > - negative, and for debug builds may be too large. */ > - int tmp; > - __asm__ ("adr %1, 1f\n\t" > - "ldr %0, [%1]\n\t" > - "add %0, %0, %1\n\t" > - "b 2f\n\t" > - ".align 2\n\t" > - "1: .word _dl_start - 1b\n\t" > - "2:" > - : "=r" (pcrel_addr), "=r" (tmp)); > -#endif > - return pcrel_addr - got_addr; > -#endif > + extern const Elf32_Ehdr __ehdr_start attribute_hidden; > + return (Elf32_Addr) &__ehdr_start; > +} > + > +/* Return the link-time address of _DYNAMIC. */ > +static __always_inline Elf32_Addr __attribute__ ((unused)) > +elf_machine_dynamic (void) > +{ > + extern Elf32_Dyn _DYNAMIC[] attribute_hidden; > + return (Elf32_Addr) _DYNAMIC - elf_machine_load_address (); > } > > static __always_inline void > diff --git a/ldso/ldso/i386/dl-sysdep.h b/ldso/ldso/i386/dl-sysdep.h > index b95328df4..8fc80a145 100644 > --- a/ldso/ldso/i386/dl-sysdep.h > +++ b/ldso/ldso/i386/dl-sysdep.h > @@ -35,28 +35,21 @@ extern unsigned long _dl_linux_resolver(struct > elf_resolve * tpnt, int reloc_ent > || (type) == R_386_TLS_TPOFF) * ELF_RTYPE_CLASS_PLT) > \ > | (((type) == R_386_COPY) * ELF_RTYPE_CLASS_COPY)) > > -/* Return the link-time address of _DYNAMIC. Conveniently, this is the > - first element of the GOT, a special entry that is never relocated. */ > -extern const Elf32_Addr _GLOBAL_OFFSET_TABLE_[] attribute_hidden; > -static __always_inline Elf32_Addr __attribute__ ((unused, const)) > -elf_machine_dynamic (void) > -{ > - /* This produces a GOTOFF reloc that resolves to zero at link time, so > in > - fact just loads from the GOT register directly. By doing it without > - an asm we can let the compiler choose any register. */ > - return _GLOBAL_OFFSET_TABLE_[0]; > -} > - > > -extern Elf32_Dyn bygotoff[] __asm__ ("_DYNAMIC") attribute_hidden; > /* Return the run-time load address of the shared object. */ > static __always_inline Elf32_Addr attribute_unused > elf_machine_load_address (void) > { > - /* Compute the difference between the runtime address of _DYNAMIC as > seen > - by a GOTOFF reference, and the link-time address found in the special > - unrelocated first GOT entry. */ > - return (Elf32_Addr) &bygotoff - elf_machine_dynamic (); > + extern const Elf32_Ehdr __ehdr_start attribute_hidden; > + return (Elf32_Addr) &__ehdr_start; > +} > + > +/* Return the link-time address of _DYNAMIC. */ > +static __always_inline Elf32_Addr __attribute__ ((unused, const)) > +elf_machine_dynamic (void) > +{ > + extern Elf32_Dyn _DYNAMIC[] attribute_hidden; > + return (Elf32_Addr) _DYNAMIC - elf_machine_load_address (); > } > > static __always_inline void > diff --git a/ldso/ldso/riscv32/dl-sysdep.h b/ldso/ldso/riscv32/dl-sysdep.h > index e0a59fddd..02296b148 100644 > --- a/ldso/ldso/riscv32/dl-sysdep.h > +++ b/ldso/ldso/riscv32/dl-sysdep.h > @@ -59,22 +59,20 @@ unsigned long _dl_linux_resolver(struct elf_resolve * > tpnt, int reloc_entry); > | (ELF_RTYPE_CLASS_COPY * ((type) == R_RISCV_COPY))) > > > -/* Return the link-time address of _DYNAMIC. */ > -static inline ElfW(Addr) > -elf_machine_dynamic (void) > -{ > - extern ElfW(Addr) _GLOBAL_OFFSET_TABLE_ __attribute__ ((visibility > ("hidden"))); > - return _GLOBAL_OFFSET_TABLE_; > -} > - > - > /* Return the run-time load address of the shared object. */ > static __always_inline ElfW(Addr) __attribute__ ((unused)) > elf_machine_load_address (void) > { > - ElfW(Addr) load_addr; > - __asm__ ("lla %0, _DYNAMIC" : "=r" (load_addr)); > - return load_addr - elf_machine_dynamic (); > + extern const ElfW(Ehdr) __ehdr_start attribute_hidden; > + return (ElfW(Addr)) &__ehdr_start; > +} > + > +/* Return the link-time address of _DYNAMIC. */ > +static inline ElfW(Addr) > +elf_machine_dynamic (void) > +{ > + extern ElfW(Dyn) _DYNAMIC[] attribute_hidden; > + return (ElfW(Addr)) _DYNAMIC - elf_machine_load_address (); > } > > static __always_inline void > diff --git a/ldso/ldso/x86_64/dl-sysdep.h b/ldso/ldso/x86_64/dl-sysdep.h > index ccf9a8851..58447a951 100644 > --- a/ldso/ldso/x86_64/dl-sysdep.h > +++ b/ldso/ldso/x86_64/dl-sysdep.h > @@ -52,48 +52,21 @@ extern unsigned long _dl_linux_resolver(struct > elf_resolve * tpnt, int reloc_ent > * ELF_RTYPE_CLASS_PLT) \ > | (((type) == R_X86_64_COPY) * ELF_RTYPE_CLASS_COPY)) > > -/* Return the link-time address of _DYNAMIC. Conveniently, this is the > - first element of the GOT. This must be inlined in a function which > - uses global data. */ > -static __always_inline Elf64_Addr __attribute__ ((unused)) > -elf_machine_dynamic (void) > -{ > - Elf64_Addr addr; > - > - /* This works because we have our GOT address available in the small PIC > - model. */ > - addr = (Elf64_Addr) &_DYNAMIC; > - > - return addr; > -} > - > > /* Return the run-time load address of the shared object. */ > static __always_inline Elf64_Addr __attribute__ ((unused)) > elf_machine_load_address (void) > { > - register Elf64_Addr addr, tmp; > - > - /* The easy way is just the same as on x86: > - leaq _dl_start, %0 > - leaq _dl_start(%%rip), %1 > - subq %0, %1 > - but this does not work with binutils since we then have > - a R_X86_64_32S relocation in a shared lib. > - > - Instead we store the address of _dl_start in the data section > - and compare it with the current value that we can get via > - an RIP relative addressing mode. */ > - > - __asm__ ("movq 1f(%%rip), %1\n" > - "0:\tleaq _dl_start(%%rip), %0\n\t" > - "subq %1, %0\n\t" > - ".section\t.data\n" > - "1:\t.quad _dl_start\n\t" > - ".previous\n\t" > - : "=r" (addr), "=r" (tmp) : : "cc"); > + extern const Elf64_Ehdr __ehdr_start attribute_hidden; > + return (Elf64_Addr) &__ehdr_start; > +} > > - return addr; > +/* Return the link-time address of _DYNAMIC. */ > +static __always_inline Elf64_Addr __attribute__ ((unused)) > +elf_machine_dynamic (void) > +{ > + extern Elf64_Dyn _DYNAMIC[] attribute_hidden; > + return (Elf64_Addr) _DYNAMIC - elf_machine_load_address (); > } > > static __always_inline void > -- > 2.47.1 > > _______________________________________________ > devel mailing list -- devel@uclibc-ng.org > To unsubscribe send an email to devel-le...@uclibc-ng.org _______________________________________________ devel mailing list -- devel@uclibc-ng.org To unsubscribe send an email to devel-le...@uclibc-ng.org
