| Message ID | 20210415061502.7248-2-damien.lemoal@wdc.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | Fix binfmt_flat loader for RISC-V | expand |
Hi Damien, On 15/4/21 4:15 pm, Damien Le Moal wrote: > Commit 2217b9826246 ("binfmt_flat: revert "binfmt_flat: don't offset > the data start"") restored offsetting the start of the data section by > a number of words defined by MAX_SHARED_LIBS. As a result, since > MAX_SHARED_LIBS is never 0, a gap between the text and data sections > always exists. For architectures which cannot support a such gap > between the text and data sections (e.g. riscv nommu), flat binary > programs cannot be executed. > > To allow an architecture to request contiguous text and data sections, > introduce the config option CONFIG_BINFMT_FLAT_NO_TEXT_DATA_GAP. > Using this new option, the macro DATA_GAP_WORDS is conditionally > defined in binfmt_flat.c to MAX_SHARED_LIBS for architectures > tolerating the text-to-data gap (CONFIG_BINFMT_FLAT_NO_TEXT_DATA_GAP > disabled case) and to 0 when CONFIG_BINFMT_FLAT_NO_TEXT_DATA_GAP is > enabled. DATA_GAP_WORDS is used in load_flat_file() to calculate the > data section length and start position. > > An architecture enabling CONFIG_BINFMT_FLAT_NO_TEXT_DATA_GAP also > prevents the use of the separate text/data load case (when the flat file > header flags FLAT_FLAG_RAM and FLAT_FLAG_GZIP are not set with NOMMU > kernels) and forces the use of a single RAM region for loading > (equivalent to FLAT_FLAG_RAM being set). So is it the case that a flat format file on RISC-V will never have relocations? > Signed-off-by: Damien Le Moal <damien.lemoal@wdc.com> > Acked-by: Palmer Dabbelt <palmerdabbelt@google.com> > --- > fs/Kconfig.binfmt | 3 +++ > fs/binfmt_flat.c | 21 +++++++++++++++------ > 2 files changed, 18 insertions(+), 6 deletions(-) > > diff --git a/fs/Kconfig.binfmt b/fs/Kconfig.binfmt > index c6f1c8c1934e..c6df931d5d45 100644 > --- a/fs/Kconfig.binfmt > +++ b/fs/Kconfig.binfmt > @@ -112,6 +112,9 @@ config BINFMT_FLAT_ARGVP_ENVP_ON_STACK > config BINFMT_FLAT_OLD_ALWAYS_RAM > bool > > +config BINFMT_FLAT_NO_TEXT_DATA_GAP > + bool > + > config BINFMT_FLAT_OLD > bool "Enable support for very old legacy flat binaries" > depends on BINFMT_FLAT > diff --git a/fs/binfmt_flat.c b/fs/binfmt_flat.c > index b9c658e0548e..2be29bb964b8 100644 > --- a/fs/binfmt_flat.c > +++ b/fs/binfmt_flat.c > @@ -74,6 +74,12 @@ > #define MAX_SHARED_LIBS (1) > #endif > > +#ifdef CONFIG_BINFMT_FLAT_NO_TEXT_DATA_GAP > +#define DATA_GAP_WORDS (0) > +#else > +#define DATA_GAP_WORDS (MAX_SHARED_LIBS) > +#endif > +> struct lib_info { > struct { > unsigned long start_code; /* Start of text segment */ > @@ -559,7 +565,10 @@ static int load_flat_file(struct linux_binprm *bprm, > * case, and then the fully copied to RAM case which lumps > * it all together. > */ > - if (!IS_ENABLED(CONFIG_MMU) && !(flags & (FLAT_FLAG_RAM|FLAT_FLAG_GZIP))) { > + if (!IS_ENABLED(CONFIG_MMU) && > + !IS_ENABLED(CONFIG_BINFMT_FLAT_NO_TEXT_DATA_GAP) && If RISC-V flat format files must always be loaded to RAM then why don't they set the FLAT_FLAG_RAM when compiled/generated? Regards Greg > + !(flags & (FLAT_FLAG_RAM|FLAT_FLAG_GZIP))) { > + > /* > * this should give us a ROM ptr, but if it doesn't we don't > * really care > @@ -576,7 +585,7 @@ static int load_flat_file(struct linux_binprm *bprm, > goto err; > } > > - len = data_len + extra + MAX_SHARED_LIBS * sizeof(unsigned long); > + len = data_len + extra + DATA_GAP_WORDS * sizeof(unsigned long); > len = PAGE_ALIGN(len); > realdatastart = vm_mmap(NULL, 0, len, > PROT_READ|PROT_WRITE|PROT_EXEC, MAP_PRIVATE, 0); > @@ -591,7 +600,7 @@ static int load_flat_file(struct linux_binprm *bprm, > goto err; > } > datapos = ALIGN(realdatastart + > - MAX_SHARED_LIBS * sizeof(unsigned long), > + DATA_GAP_WORDS * sizeof(unsigned long), > FLAT_DATA_ALIGN); > > pr_debug("Allocated data+bss+stack (%u bytes): %lx\n", > @@ -622,7 +631,7 @@ static int load_flat_file(struct linux_binprm *bprm, > memp_size = len; > } else { > > - len = text_len + data_len + extra + MAX_SHARED_LIBS * sizeof(u32); > + len = text_len + data_len + extra + DATA_GAP_WORDS * sizeof(u32); > len = PAGE_ALIGN(len); > textpos = vm_mmap(NULL, 0, len, > PROT_READ | PROT_EXEC | PROT_WRITE, MAP_PRIVATE, 0); > @@ -638,7 +647,7 @@ static int load_flat_file(struct linux_binprm *bprm, > > realdatastart = textpos + ntohl(hdr->data_start); > datapos = ALIGN(realdatastart + > - MAX_SHARED_LIBS * sizeof(u32), > + DATA_GAP_WORDS * sizeof(u32), > FLAT_DATA_ALIGN); > > reloc = (__be32 __user *) > @@ -714,7 +723,7 @@ static int load_flat_file(struct linux_binprm *bprm, > ret = result; > pr_err("Unable to read code+data+bss, errno %d\n", ret); > vm_munmap(textpos, text_len + data_len + extra + > - MAX_SHARED_LIBS * sizeof(u32)); > + DATA_GAP_WORDS * sizeof(u32)); > goto err; > } > } >
On 2021/04/15 23:04, Greg Ungerer wrote: > Hi Damien, > > On 15/4/21 4:15 pm, Damien Le Moal wrote: >> Commit 2217b9826246 ("binfmt_flat: revert "binfmt_flat: don't offset >> the data start"") restored offsetting the start of the data section by >> a number of words defined by MAX_SHARED_LIBS. As a result, since >> MAX_SHARED_LIBS is never 0, a gap between the text and data sections >> always exists. For architectures which cannot support a such gap >> between the text and data sections (e.g. riscv nommu), flat binary >> programs cannot be executed. >> >> To allow an architecture to request contiguous text and data sections, >> introduce the config option CONFIG_BINFMT_FLAT_NO_TEXT_DATA_GAP. >> Using this new option, the macro DATA_GAP_WORDS is conditionally >> defined in binfmt_flat.c to MAX_SHARED_LIBS for architectures >> tolerating the text-to-data gap (CONFIG_BINFMT_FLAT_NO_TEXT_DATA_GAP >> disabled case) and to 0 when CONFIG_BINFMT_FLAT_NO_TEXT_DATA_GAP is >> enabled. DATA_GAP_WORDS is used in load_flat_file() to calculate the >> data section length and start position. >> >> An architecture enabling CONFIG_BINFMT_FLAT_NO_TEXT_DATA_GAP also >> prevents the use of the separate text/data load case (when the flat file >> header flags FLAT_FLAG_RAM and FLAT_FLAG_GZIP are not set with NOMMU >> kernels) and forces the use of a single RAM region for loading >> (equivalent to FLAT_FLAG_RAM being set). > > So is it the case that a flat format file on RISC-V will never have > relocations? No, it does have relocations. But there is no entry for the global pointer (__global_pointer$) location. This is because the loading of that value in the gp register in the C-library crt1.S is done using a PC-relative instruction. The value for it is resolved at compile time and does not get a relocation table entry. Other functions calls and symbol references do have relocation table entries, so the binary can be loaded anywhere. The missing relocation for the global pointer mandates that text and data be loaded at the same positions relative to each other that the linker file defines. Otherwise, loading of __global_pointer$ into the gp register (first thing that C libraries crt1.S do) result in a garbage value being loaded. I tried some tricks with the linker file and changing uclibc crt1.S to have the gp loading done using a symbol address instead of a PC-relative offset. I could then see a relocation table entry for that symbol. That still did not work as I was probably doing something wrong. Anyway, such solution requires changing a lot of things in C libraries loading assembler that is common between NOMMU and MMU code. Changing it would break MMU enabled programs. >> Signed-off-by: Damien Le Moal <damien.lemoal@wdc.com> >> Acked-by: Palmer Dabbelt <palmerdabbelt@google.com> >> --- >> fs/Kconfig.binfmt | 3 +++ >> fs/binfmt_flat.c | 21 +++++++++++++++------ >> 2 files changed, 18 insertions(+), 6 deletions(-) >> >> diff --git a/fs/Kconfig.binfmt b/fs/Kconfig.binfmt >> index c6f1c8c1934e..c6df931d5d45 100644 >> --- a/fs/Kconfig.binfmt >> +++ b/fs/Kconfig.binfmt >> @@ -112,6 +112,9 @@ config BINFMT_FLAT_ARGVP_ENVP_ON_STACK >> config BINFMT_FLAT_OLD_ALWAYS_RAM >> bool >> >> +config BINFMT_FLAT_NO_TEXT_DATA_GAP >> + bool >> + >> config BINFMT_FLAT_OLD >> bool "Enable support for very old legacy flat binaries" >> depends on BINFMT_FLAT >> diff --git a/fs/binfmt_flat.c b/fs/binfmt_flat.c >> index b9c658e0548e..2be29bb964b8 100644 >> --- a/fs/binfmt_flat.c >> +++ b/fs/binfmt_flat.c >> @@ -74,6 +74,12 @@ >> #define MAX_SHARED_LIBS (1) >> #endif >> >> +#ifdef CONFIG_BINFMT_FLAT_NO_TEXT_DATA_GAP >> +#define DATA_GAP_WORDS (0) >> +#else >> +#define DATA_GAP_WORDS (MAX_SHARED_LIBS) >> +#endif >> +> struct lib_info { >> struct { >> unsigned long start_code; /* Start of text segment */ >> @@ -559,7 +565,10 @@ static int load_flat_file(struct linux_binprm *bprm, >> * case, and then the fully copied to RAM case which lumps >> * it all together. >> */ >> - if (!IS_ENABLED(CONFIG_MMU) && !(flags & (FLAT_FLAG_RAM|FLAT_FLAG_GZIP))) { >> + if (!IS_ENABLED(CONFIG_MMU) && >> + !IS_ENABLED(CONFIG_BINFMT_FLAT_NO_TEXT_DATA_GAP) && > > If RISC-V flat format files must always be loaded to RAM then why don't > they set the FLAT_FLAG_RAM when compiled/generated? That is done. The patch I have for elf2flt sets it. Coding it like this here is I think safer (whatever the userspace toolchain did, the kernel assumes FLAT_FLAG_RAM). And it also has the nice side effect to suppress the first part of the if () in the final binary. Smaller code size :) > > Regards > Greg > > >> + !(flags & (FLAT_FLAG_RAM|FLAT_FLAG_GZIP))) { >> + >> /* >> * this should give us a ROM ptr, but if it doesn't we don't >> * really care >> @@ -576,7 +585,7 @@ static int load_flat_file(struct linux_binprm *bprm, >> goto err; >> } >> >> - len = data_len + extra + MAX_SHARED_LIBS * sizeof(unsigned long); >> + len = data_len + extra + DATA_GAP_WORDS * sizeof(unsigned long); >> len = PAGE_ALIGN(len); >> realdatastart = vm_mmap(NULL, 0, len, >> PROT_READ|PROT_WRITE|PROT_EXEC, MAP_PRIVATE, 0); >> @@ -591,7 +600,7 @@ static int load_flat_file(struct linux_binprm *bprm, >> goto err; >> } >> datapos = ALIGN(realdatastart + >> - MAX_SHARED_LIBS * sizeof(unsigned long), >> + DATA_GAP_WORDS * sizeof(unsigned long), >> FLAT_DATA_ALIGN); >> >> pr_debug("Allocated data+bss+stack (%u bytes): %lx\n", >> @@ -622,7 +631,7 @@ static int load_flat_file(struct linux_binprm *bprm, >> memp_size = len; >> } else { >> >> - len = text_len + data_len + extra + MAX_SHARED_LIBS * sizeof(u32); >> + len = text_len + data_len + extra + DATA_GAP_WORDS * sizeof(u32); >> len = PAGE_ALIGN(len); >> textpos = vm_mmap(NULL, 0, len, >> PROT_READ | PROT_EXEC | PROT_WRITE, MAP_PRIVATE, 0); >> @@ -638,7 +647,7 @@ static int load_flat_file(struct linux_binprm *bprm, >> >> realdatastart = textpos + ntohl(hdr->data_start); >> datapos = ALIGN(realdatastart + >> - MAX_SHARED_LIBS * sizeof(u32), >> + DATA_GAP_WORDS * sizeof(u32), >> FLAT_DATA_ALIGN); >> >> reloc = (__be32 __user *) >> @@ -714,7 +723,7 @@ static int load_flat_file(struct linux_binprm *bprm, >> ret = result; >> pr_err("Unable to read code+data+bss, errno %d\n", ret); >> vm_munmap(textpos, text_len + data_len + extra + >> - MAX_SHARED_LIBS * sizeof(u32)); >> + DATA_GAP_WORDS * sizeof(u32)); >> goto err; >> } >> } >> >
On 16/4/21 9:22 am, Damien Le Moal wrote: > On 2021/04/15 23:04, Greg Ungerer wrote: >> Hi Damien, >> >> On 15/4/21 4:15 pm, Damien Le Moal wrote: >>> Commit 2217b9826246 ("binfmt_flat: revert "binfmt_flat: don't offset >>> the data start"") restored offsetting the start of the data section by >>> a number of words defined by MAX_SHARED_LIBS. As a result, since >>> MAX_SHARED_LIBS is never 0, a gap between the text and data sections >>> always exists. For architectures which cannot support a such gap >>> between the text and data sections (e.g. riscv nommu), flat binary >>> programs cannot be executed. >>> >>> To allow an architecture to request contiguous text and data sections, >>> introduce the config option CONFIG_BINFMT_FLAT_NO_TEXT_DATA_GAP. >>> Using this new option, the macro DATA_GAP_WORDS is conditionally >>> defined in binfmt_flat.c to MAX_SHARED_LIBS for architectures >>> tolerating the text-to-data gap (CONFIG_BINFMT_FLAT_NO_TEXT_DATA_GAP >>> disabled case) and to 0 when CONFIG_BINFMT_FLAT_NO_TEXT_DATA_GAP is >>> enabled. DATA_GAP_WORDS is used in load_flat_file() to calculate the >>> data section length and start position. >>> >>> An architecture enabling CONFIG_BINFMT_FLAT_NO_TEXT_DATA_GAP also >>> prevents the use of the separate text/data load case (when the flat file >>> header flags FLAT_FLAG_RAM and FLAT_FLAG_GZIP are not set with NOMMU >>> kernels) and forces the use of a single RAM region for loading >>> (equivalent to FLAT_FLAG_RAM being set). >> >> So is it the case that a flat format file on RISC-V will never have >> relocations? > > No, it does have relocations. But there is no entry for the global pointer > (__global_pointer$) location. This is because the loading of that value in the > gp register in the C-library crt1.S is done using a PC-relative instruction. The > value for it is resolved at compile time and does not get a relocation table > entry. Other functions calls and symbol references do have relocation table > entries, so the binary can be loaded anywhere. The missing relocation for the > global pointer mandates that text and data be loaded at the same positions > relative to each other that the linker file defines. Otherwise, loading of > __global_pointer$ into the gp register (first thing that C libraries crt1.S do) > result in a garbage value being loaded. > > I tried some tricks with the linker file and changing uclibc crt1.S to have the > gp loading done using a symbol address instead of a PC-relative offset. I could > then see a relocation table entry for that symbol. That still did not work as I > was probably doing something wrong. Anyway, such solution requires changing a > lot of things in C libraries loading assembler that is common between NOMMU and > MMU code. Changing it would break MMU enabled programs. > > >>> Signed-off-by: Damien Le Moal <damien.lemoal@wdc.com> >>> Acked-by: Palmer Dabbelt <palmerdabbelt@google.com> >>> --- >>> fs/Kconfig.binfmt | 3 +++ >>> fs/binfmt_flat.c | 21 +++++++++++++++------ >>> 2 files changed, 18 insertions(+), 6 deletions(-) >>> >>> diff --git a/fs/Kconfig.binfmt b/fs/Kconfig.binfmt >>> index c6f1c8c1934e..c6df931d5d45 100644 >>> --- a/fs/Kconfig.binfmt >>> +++ b/fs/Kconfig.binfmt >>> @@ -112,6 +112,9 @@ config BINFMT_FLAT_ARGVP_ENVP_ON_STACK >>> config BINFMT_FLAT_OLD_ALWAYS_RAM >>> bool >>> >>> +config BINFMT_FLAT_NO_TEXT_DATA_GAP >>> + bool >>> + >>> config BINFMT_FLAT_OLD >>> bool "Enable support for very old legacy flat binaries" >>> depends on BINFMT_FLAT >>> diff --git a/fs/binfmt_flat.c b/fs/binfmt_flat.c >>> index b9c658e0548e..2be29bb964b8 100644 >>> --- a/fs/binfmt_flat.c >>> +++ b/fs/binfmt_flat.c >>> @@ -74,6 +74,12 @@ >>> #define MAX_SHARED_LIBS (1) >>> #endif >>> >>> +#ifdef CONFIG_BINFMT_FLAT_NO_TEXT_DATA_GAP >>> +#define DATA_GAP_WORDS (0) >>> +#else >>> +#define DATA_GAP_WORDS (MAX_SHARED_LIBS) >>> +#endif >>> +> struct lib_info { >>> struct { >>> unsigned long start_code; /* Start of text segment */ >>> @@ -559,7 +565,10 @@ static int load_flat_file(struct linux_binprm *bprm, >>> * case, and then the fully copied to RAM case which lumps >>> * it all together. >>> */ >>> - if (!IS_ENABLED(CONFIG_MMU) && !(flags & (FLAT_FLAG_RAM|FLAT_FLAG_GZIP))) { >>> + if (!IS_ENABLED(CONFIG_MMU) && >>> + !IS_ENABLED(CONFIG_BINFMT_FLAT_NO_TEXT_DATA_GAP) && >> >> If RISC-V flat format files must always be loaded to RAM then why don't >> they set the FLAT_FLAG_RAM when compiled/generated? > > That is done. The patch I have for elf2flt sets it. Coding it like this here is > I think safer (whatever the userspace toolchain did, the kernel assumes > FLAT_FLAG_RAM). And it also has the nice side effect to suppress the first part > of the if () in the final binary. Smaller code size :) My concern here is that CONFIG_BINFMT_FLAT_NO_TEXT_DATA_GA being enabled doesn't just in itself mean you need to force a RAM load. It is just in the RISC-V case it currently does. And it may change in the future. The considerable RAM savings you get from supporting a separate data segment to code segment means there is motivation to create tooling and code generation to support it. I don't feel that strongly about it, but this code is obtuse enough already. No need to make it worse if we don't have too. Regards Greg >>> + !(flags & (FLAT_FLAG_RAM|FLAT_FLAG_GZIP))) { >>> + >>> /* >>> * this should give us a ROM ptr, but if it doesn't we don't >>> * really care >>> @@ -576,7 +585,7 @@ static int load_flat_file(struct linux_binprm *bprm, >>> goto err; >>> } >>> >>> - len = data_len + extra + MAX_SHARED_LIBS * sizeof(unsigned long); >>> + len = data_len + extra + DATA_GAP_WORDS * sizeof(unsigned long); >>> len = PAGE_ALIGN(len); >>> realdatastart = vm_mmap(NULL, 0, len, >>> PROT_READ|PROT_WRITE|PROT_EXEC, MAP_PRIVATE, 0); >>> @@ -591,7 +600,7 @@ static int load_flat_file(struct linux_binprm *bprm, >>> goto err; >>> } >>> datapos = ALIGN(realdatastart + >>> - MAX_SHARED_LIBS * sizeof(unsigned long), >>> + DATA_GAP_WORDS * sizeof(unsigned long), >>> FLAT_DATA_ALIGN); >>> >>> pr_debug("Allocated data+bss+stack (%u bytes): %lx\n", >>> @@ -622,7 +631,7 @@ static int load_flat_file(struct linux_binprm *bprm, >>> memp_size = len; >>> } else { >>> >>> - len = text_len + data_len + extra + MAX_SHARED_LIBS * sizeof(u32); >>> + len = text_len + data_len + extra + DATA_GAP_WORDS * sizeof(u32); >>> len = PAGE_ALIGN(len); >>> textpos = vm_mmap(NULL, 0, len, >>> PROT_READ | PROT_EXEC | PROT_WRITE, MAP_PRIVATE, 0); >>> @@ -638,7 +647,7 @@ static int load_flat_file(struct linux_binprm *bprm, >>> >>> realdatastart = textpos + ntohl(hdr->data_start); >>> datapos = ALIGN(realdatastart + >>> - MAX_SHARED_LIBS * sizeof(u32), >>> + DATA_GAP_WORDS * sizeof(u32), >>> FLAT_DATA_ALIGN); >>> >>> reloc = (__be32 __user *) >>> @@ -714,7 +723,7 @@ static int load_flat_file(struct linux_binprm *bprm, >>> ret = result; >>> pr_err("Unable to read code+data+bss, errno %d\n", ret); >>> vm_munmap(textpos, text_len + data_len + extra + >>> - MAX_SHARED_LIBS * sizeof(u32)); >>> + DATA_GAP_WORDS * sizeof(u32)); >>> goto err; >>> } >>> } >>> >> > >
On 2021/04/16 16:24, Greg Ungerer wrote: > > On 16/4/21 9:22 am, Damien Le Moal wrote: >> On 2021/04/15 23:04, Greg Ungerer wrote: >>> Hi Damien, >>> >>> On 15/4/21 4:15 pm, Damien Le Moal wrote: >>>> Commit 2217b9826246 ("binfmt_flat: revert "binfmt_flat: don't offset >>>> the data start"") restored offsetting the start of the data section by >>>> a number of words defined by MAX_SHARED_LIBS. As a result, since >>>> MAX_SHARED_LIBS is never 0, a gap between the text and data sections >>>> always exists. For architectures which cannot support a such gap >>>> between the text and data sections (e.g. riscv nommu), flat binary >>>> programs cannot be executed. >>>> >>>> To allow an architecture to request contiguous text and data sections, >>>> introduce the config option CONFIG_BINFMT_FLAT_NO_TEXT_DATA_GAP. >>>> Using this new option, the macro DATA_GAP_WORDS is conditionally >>>> defined in binfmt_flat.c to MAX_SHARED_LIBS for architectures >>>> tolerating the text-to-data gap (CONFIG_BINFMT_FLAT_NO_TEXT_DATA_GAP >>>> disabled case) and to 0 when CONFIG_BINFMT_FLAT_NO_TEXT_DATA_GAP is >>>> enabled. DATA_GAP_WORDS is used in load_flat_file() to calculate the >>>> data section length and start position. >>>> >>>> An architecture enabling CONFIG_BINFMT_FLAT_NO_TEXT_DATA_GAP also >>>> prevents the use of the separate text/data load case (when the flat file >>>> header flags FLAT_FLAG_RAM and FLAT_FLAG_GZIP are not set with NOMMU >>>> kernels) and forces the use of a single RAM region for loading >>>> (equivalent to FLAT_FLAG_RAM being set). >>> >>> So is it the case that a flat format file on RISC-V will never have >>> relocations? >> >> No, it does have relocations. But there is no entry for the global pointer >> (__global_pointer$) location. This is because the loading of that value in the >> gp register in the C-library crt1.S is done using a PC-relative instruction. The >> value for it is resolved at compile time and does not get a relocation table >> entry. Other functions calls and symbol references do have relocation table >> entries, so the binary can be loaded anywhere. The missing relocation for the >> global pointer mandates that text and data be loaded at the same positions >> relative to each other that the linker file defines. Otherwise, loading of >> __global_pointer$ into the gp register (first thing that C libraries crt1.S do) >> result in a garbage value being loaded. >> >> I tried some tricks with the linker file and changing uclibc crt1.S to have the >> gp loading done using a symbol address instead of a PC-relative offset. I could >> then see a relocation table entry for that symbol. That still did not work as I >> was probably doing something wrong. Anyway, such solution requires changing a >> lot of things in C libraries loading assembler that is common between NOMMU and >> MMU code. Changing it would break MMU enabled programs. >> >> >>>> Signed-off-by: Damien Le Moal <damien.lemoal@wdc.com> >>>> Acked-by: Palmer Dabbelt <palmerdabbelt@google.com> >>>> --- >>>> fs/Kconfig.binfmt | 3 +++ >>>> fs/binfmt_flat.c | 21 +++++++++++++++------ >>>> 2 files changed, 18 insertions(+), 6 deletions(-) >>>> >>>> diff --git a/fs/Kconfig.binfmt b/fs/Kconfig.binfmt >>>> index c6f1c8c1934e..c6df931d5d45 100644 >>>> --- a/fs/Kconfig.binfmt >>>> +++ b/fs/Kconfig.binfmt >>>> @@ -112,6 +112,9 @@ config BINFMT_FLAT_ARGVP_ENVP_ON_STACK >>>> config BINFMT_FLAT_OLD_ALWAYS_RAM >>>> bool >>>> >>>> +config BINFMT_FLAT_NO_TEXT_DATA_GAP >>>> + bool >>>> + >>>> config BINFMT_FLAT_OLD >>>> bool "Enable support for very old legacy flat binaries" >>>> depends on BINFMT_FLAT >>>> diff --git a/fs/binfmt_flat.c b/fs/binfmt_flat.c >>>> index b9c658e0548e..2be29bb964b8 100644 >>>> --- a/fs/binfmt_flat.c >>>> +++ b/fs/binfmt_flat.c >>>> @@ -74,6 +74,12 @@ >>>> #define MAX_SHARED_LIBS (1) >>>> #endif >>>> >>>> +#ifdef CONFIG_BINFMT_FLAT_NO_TEXT_DATA_GAP >>>> +#define DATA_GAP_WORDS (0) >>>> +#else >>>> +#define DATA_GAP_WORDS (MAX_SHARED_LIBS) >>>> +#endif >>>> +> struct lib_info { >>>> struct { >>>> unsigned long start_code; /* Start of text segment */ >>>> @@ -559,7 +565,10 @@ static int load_flat_file(struct linux_binprm *bprm, >>>> * case, and then the fully copied to RAM case which lumps >>>> * it all together. >>>> */ >>>> - if (!IS_ENABLED(CONFIG_MMU) && !(flags & (FLAT_FLAG_RAM|FLAT_FLAG_GZIP))) { >>>> + if (!IS_ENABLED(CONFIG_MMU) && >>>> + !IS_ENABLED(CONFIG_BINFMT_FLAT_NO_TEXT_DATA_GAP) && >>> >>> If RISC-V flat format files must always be loaded to RAM then why don't >>> they set the FLAT_FLAG_RAM when compiled/generated? >> >> That is done. The patch I have for elf2flt sets it. Coding it like this here is >> I think safer (whatever the userspace toolchain did, the kernel assumes >> FLAT_FLAG_RAM). And it also has the nice side effect to suppress the first part >> of the if () in the final binary. Smaller code size :) > > My concern here is that CONFIG_BINFMT_FLAT_NO_TEXT_DATA_GA being > enabled doesn't just in itself mean you need to force a RAM load. > It is just in the RISC-V case it currently does. Good point. > > And it may change in the future. The considerable RAM savings > you get from supporting a separate data segment to code segment > means there is motivation to create tooling and code generation > to support it. Totally agree here. And I did try hard to get it to work... > > I don't feel that strongly about it, but this code is obtuse enough already. > No need to make it worse if we don't have too. I see your point. I will remove that !IS_ENABLED(CONFIG_BINFMT_FLAT_NO_TEXT_DATA_GAP) from the top if() condition. Without it, fixing the toolchain etc will indeed not require patching again the kernel. Sending a v4. > > Regards > Greg > > > >>>> + !(flags & (FLAT_FLAG_RAM|FLAT_FLAG_GZIP))) { >>>> + >>>> /* >>>> * this should give us a ROM ptr, but if it doesn't we don't >>>> * really care >>>> @@ -576,7 +585,7 @@ static int load_flat_file(struct linux_binprm *bprm, >>>> goto err; >>>> } >>>> >>>> - len = data_len + extra + MAX_SHARED_LIBS * sizeof(unsigned long); >>>> + len = data_len + extra + DATA_GAP_WORDS * sizeof(unsigned long); >>>> len = PAGE_ALIGN(len); >>>> realdatastart = vm_mmap(NULL, 0, len, >>>> PROT_READ|PROT_WRITE|PROT_EXEC, MAP_PRIVATE, 0); >>>> @@ -591,7 +600,7 @@ static int load_flat_file(struct linux_binprm *bprm, >>>> goto err; >>>> } >>>> datapos = ALIGN(realdatastart + >>>> - MAX_SHARED_LIBS * sizeof(unsigned long), >>>> + DATA_GAP_WORDS * sizeof(unsigned long), >>>> FLAT_DATA_ALIGN); >>>> >>>> pr_debug("Allocated data+bss+stack (%u bytes): %lx\n", >>>> @@ -622,7 +631,7 @@ static int load_flat_file(struct linux_binprm *bprm, >>>> memp_size = len; >>>> } else { >>>> >>>> - len = text_len + data_len + extra + MAX_SHARED_LIBS * sizeof(u32); >>>> + len = text_len + data_len + extra + DATA_GAP_WORDS * sizeof(u32); >>>> len = PAGE_ALIGN(len); >>>> textpos = vm_mmap(NULL, 0, len, >>>> PROT_READ | PROT_EXEC | PROT_WRITE, MAP_PRIVATE, 0); >>>> @@ -638,7 +647,7 @@ static int load_flat_file(struct linux_binprm *bprm, >>>> >>>> realdatastart = textpos + ntohl(hdr->data_start); >>>> datapos = ALIGN(realdatastart + >>>> - MAX_SHARED_LIBS * sizeof(u32), >>>> + DATA_GAP_WORDS * sizeof(u32), >>>> FLAT_DATA_ALIGN); >>>> >>>> reloc = (__be32 __user *) >>>> @@ -714,7 +723,7 @@ static int load_flat_file(struct linux_binprm *bprm, >>>> ret = result; >>>> pr_err("Unable to read code+data+bss, errno %d\n", ret); >>>> vm_munmap(textpos, text_len + data_len + extra + >>>> - MAX_SHARED_LIBS * sizeof(u32)); >>>> + DATA_GAP_WORDS * sizeof(u32)); >>>> goto err; >>>> } >>>> } >>>> >>> >> >> >
diff --git a/fs/Kconfig.binfmt b/fs/Kconfig.binfmt index c6f1c8c1934e..c6df931d5d45 100644 --- a/fs/Kconfig.binfmt +++ b/fs/Kconfig.binfmt @@ -112,6 +112,9 @@ config BINFMT_FLAT_ARGVP_ENVP_ON_STACK config BINFMT_FLAT_OLD_ALWAYS_RAM bool +config BINFMT_FLAT_NO_TEXT_DATA_GAP + bool + config BINFMT_FLAT_OLD bool "Enable support for very old legacy flat binaries" depends on BINFMT_FLAT diff --git a/fs/binfmt_flat.c b/fs/binfmt_flat.c index b9c658e0548e..2be29bb964b8 100644 --- a/fs/binfmt_flat.c +++ b/fs/binfmt_flat.c @@ -74,6 +74,12 @@ #define MAX_SHARED_LIBS (1) #endif +#ifdef CONFIG_BINFMT_FLAT_NO_TEXT_DATA_GAP +#define DATA_GAP_WORDS (0) +#else +#define DATA_GAP_WORDS (MAX_SHARED_LIBS) +#endif + struct lib_info { struct { unsigned long start_code; /* Start of text segment */ @@ -559,7 +565,10 @@ static int load_flat_file(struct linux_binprm *bprm, * case, and then the fully copied to RAM case which lumps * it all together. */ - if (!IS_ENABLED(CONFIG_MMU) && !(flags & (FLAT_FLAG_RAM|FLAT_FLAG_GZIP))) { + if (!IS_ENABLED(CONFIG_MMU) && + !IS_ENABLED(CONFIG_BINFMT_FLAT_NO_TEXT_DATA_GAP) && + !(flags & (FLAT_FLAG_RAM|FLAT_FLAG_GZIP))) { + /* * this should give us a ROM ptr, but if it doesn't we don't * really care @@ -576,7 +585,7 @@ static int load_flat_file(struct linux_binprm *bprm, goto err; } - len = data_len + extra + MAX_SHARED_LIBS * sizeof(unsigned long); + len = data_len + extra + DATA_GAP_WORDS * sizeof(unsigned long); len = PAGE_ALIGN(len); realdatastart = vm_mmap(NULL, 0, len, PROT_READ|PROT_WRITE|PROT_EXEC, MAP_PRIVATE, 0); @@ -591,7 +600,7 @@ static int load_flat_file(struct linux_binprm *bprm, goto err; } datapos = ALIGN(realdatastart + - MAX_SHARED_LIBS * sizeof(unsigned long), + DATA_GAP_WORDS * sizeof(unsigned long), FLAT_DATA_ALIGN); pr_debug("Allocated data+bss+stack (%u bytes): %lx\n", @@ -622,7 +631,7 @@ static int load_flat_file(struct linux_binprm *bprm, memp_size = len; } else { - len = text_len + data_len + extra + MAX_SHARED_LIBS * sizeof(u32); + len = text_len + data_len + extra + DATA_GAP_WORDS * sizeof(u32); len = PAGE_ALIGN(len); textpos = vm_mmap(NULL, 0, len, PROT_READ | PROT_EXEC | PROT_WRITE, MAP_PRIVATE, 0); @@ -638,7 +647,7 @@ static int load_flat_file(struct linux_binprm *bprm, realdatastart = textpos + ntohl(hdr->data_start); datapos = ALIGN(realdatastart + - MAX_SHARED_LIBS * sizeof(u32), + DATA_GAP_WORDS * sizeof(u32), FLAT_DATA_ALIGN); reloc = (__be32 __user *) @@ -714,7 +723,7 @@ static int load_flat_file(struct linux_binprm *bprm, ret = result; pr_err("Unable to read code+data+bss, errno %d\n", ret); vm_munmap(textpos, text_len + data_len + extra + - MAX_SHARED_LIBS * sizeof(u32)); + DATA_GAP_WORDS * sizeof(u32)); goto err; } }
Commit 2217b9826246 ("binfmt_flat: revert "binfmt_flat: don't offset the data start"") restored offsetting the start of the data section by a number of words defined by MAX_SHARED_LIBS. As a result, since MAX_SHARED_LIBS is never 0, a gap between the text and data sections always exists. For architectures which cannot support a such gap between the text and data sections (e.g. riscv nommu), flat binary programs cannot be executed. To allow an architecture to request contiguous text and data sections, introduce the config option CONFIG_BINFMT_FLAT_NO_TEXT_DATA_GAP. Using this new option, the macro DATA_GAP_WORDS is conditionally defined in binfmt_flat.c to MAX_SHARED_LIBS for architectures tolerating the text-to-data gap (CONFIG_BINFMT_FLAT_NO_TEXT_DATA_GAP disabled case) and to 0 when CONFIG_BINFMT_FLAT_NO_TEXT_DATA_GAP is enabled. DATA_GAP_WORDS is used in load_flat_file() to calculate the data section length and start position. An architecture enabling CONFIG_BINFMT_FLAT_NO_TEXT_DATA_GAP also prevents the use of the separate text/data load case (when the flat file header flags FLAT_FLAG_RAM and FLAT_FLAG_GZIP are not set with NOMMU kernels) and forces the use of a single RAM region for loading (equivalent to FLAT_FLAG_RAM being set). Signed-off-by: Damien Le Moal <damien.lemoal@wdc.com> Acked-by: Palmer Dabbelt <palmerdabbelt@google.com> --- fs/Kconfig.binfmt | 3 +++ fs/binfmt_flat.c | 21 +++++++++++++++------ 2 files changed, 18 insertions(+), 6 deletions(-)