Message ID | 20230504-never-childlike-75e2ce7e50d8@spud (mailing list archive) |
---|---|
State | Superseded |
Delegated to: | Palmer Dabbelt |
Headers | show |
Series | ISA string parser cleanups++ | expand |
Context | Check | Description |
---|---|---|
conchuod/tree_selection | fail | Failed to apply to next/pending-fixes or riscv/for-next |
On Thu, May 04, 2023 at 07:14:24PM +0100, Conor Dooley wrote: > From: Conor Dooley <conor.dooley@microchip.com> > > I have found these comments to not be at all helpful whenever I look at > the parser. Further, the comments in the default case (single letter > parser) are not quite right either. > Group the comments into a larger one at the start of each case, that > attempts to explain things at a higher level. > > Signed-off-by: Conor Dooley <conor.dooley@microchip.com> > --- > arch/riscv/kernel/cpufeature.c | 71 ++++++++++++++++++++++++++++------ > 1 file changed, 60 insertions(+), 11 deletions(-) > > diff --git a/arch/riscv/kernel/cpufeature.c b/arch/riscv/kernel/cpufeature.c > index a79c5c52a174..2fc72f092057 100644 > --- a/arch/riscv/kernel/cpufeature.c > +++ b/arch/riscv/kernel/cpufeature.c > @@ -146,7 +146,7 @@ void __init riscv_fill_hwcap(void) > > switch (*ext) { > case 's': > - /** > + /* > * Workaround for invalid single-letter 's' & 'u'(QEMU). > * No need to set the bit in riscv_isa as 's' & 'u' are > * not valid ISA extensions. It works until multi-letter > @@ -163,53 +163,102 @@ void __init riscv_fill_hwcap(void) > case 'X': > case 'z': > case 'Z': > + /* > + * Before attempting to parse the extension itself, we find its end. > + * As multi-letter extensions must be split from other multi-letter > + * extensions with an "_", the end of a multi-letter extension will > + * either be the null character as of_property_read_string() returns > + * null-terminated strings, The ACPI table also requires the ISA string be null-terminated. I'd maybe drop the reference to the DT function and just state the string will be null-terminated to avoid any ACPI concern. > or the "_" at the start of the next > + * multi-letter extension. > + * > + * Next, as the extensions version is currently ignored, we > + * eliminate that portion. This is done by parsing backwards from > + * the end of the extension, removing any numbers. This may be a > + * major or minor number however, so the process is repeated if a > + * minor number was found. > + * > + * ext_end is intended to represent the first character *after* the > + * name portion of an extension, but will be decremented to the last > + * character itself while eliminating the extensions version number. > + * A simple re-increment solves this problem. > + */ > ext_long = true; > - /* Multi-letter extension must be delimited */ > for (; *isa && *isa != '_'; ++isa) > if (unlikely(!isalnum(*isa))) > ext_err = true; > - /* Parse backwards */ > + > ext_end = isa; > if (unlikely(ext_err)) > break; > + > if (!isdigit(ext_end[-1])) > break; > - /* Skip the minor version */ > + > while (isdigit(*--ext_end)) > ; > - if (tolower(ext_end[0]) != 'p' > - || !isdigit(ext_end[-1])) { > - /* Advance it to offset the pre-decrement */ > + > + if (tolower(ext_end[0]) != 'p' || !isdigit(ext_end[-1])) { > ++ext_end; > break; > } > - /* Skip the major version */ > + > while (isdigit(*--ext_end)) > ; > + > ++ext_end; > break; > default: > + /* > + * Things are a little easier for single-letter extensions, as they > + * are parsed forwards. > + * > + * After checking that our starting position is valid, we need to > + * ensure that, when isa was incremented at the start of the loop, > + * that it arrived at the start of the next extension. > + * > + * If we are already on a non-digit, there is nothing to do. Either > + * we have a multi-letter extension's _, or the start of an > + * extension. > + * > + * Otherwise we have found the current extension's major version > + * number. Parse past it, and a subsequent p/minor version number > + * if present. The `p` extension must not appear immediately after > + * a number, so there is no fear of missing it. > + * > + */ > if (unlikely(!isalpha(*ext))) { > ext_err = true; > break; > } > - /* Find next extension */ > + > if (!isdigit(*isa)) > break; > - /* Skip the minor version */ > + > while (isdigit(*++isa)) > ; > + > if (tolower(*isa) != 'p') > break; > + > if (!isdigit(*++isa)) { > --isa; > break; > } > - /* Skip the major version */ > + > while (isdigit(*++isa)) > ; > + > break; > } > + > + /* > + * The parser expects that at the start of an iteration isa points to the > + * character before the start of the next extension. This will not be the > + * case if we have just parsed a single-letter extension and the next > + * extension is not a multi-letter extension prefixed with an "_". It is > + * also not the case at the end of the string, where it will point to the > + * terminating null character. > + */ > if (*isa != '_') > --isa; > > -- > 2.39.2 > Reviewed-by: Andrew Jones <ajones@ventanamicro.com> Thanks, drew
diff --git a/arch/riscv/kernel/cpufeature.c b/arch/riscv/kernel/cpufeature.c index a79c5c52a174..2fc72f092057 100644 --- a/arch/riscv/kernel/cpufeature.c +++ b/arch/riscv/kernel/cpufeature.c @@ -146,7 +146,7 @@ void __init riscv_fill_hwcap(void) switch (*ext) { case 's': - /** + /* * Workaround for invalid single-letter 's' & 'u'(QEMU). * No need to set the bit in riscv_isa as 's' & 'u' are * not valid ISA extensions. It works until multi-letter @@ -163,53 +163,102 @@ void __init riscv_fill_hwcap(void) case 'X': case 'z': case 'Z': + /* + * Before attempting to parse the extension itself, we find its end. + * As multi-letter extensions must be split from other multi-letter + * extensions with an "_", the end of a multi-letter extension will + * either be the null character as of_property_read_string() returns + * null-terminated strings, or the "_" at the start of the next + * multi-letter extension. + * + * Next, as the extensions version is currently ignored, we + * eliminate that portion. This is done by parsing backwards from + * the end of the extension, removing any numbers. This may be a + * major or minor number however, so the process is repeated if a + * minor number was found. + * + * ext_end is intended to represent the first character *after* the + * name portion of an extension, but will be decremented to the last + * character itself while eliminating the extensions version number. + * A simple re-increment solves this problem. + */ ext_long = true; - /* Multi-letter extension must be delimited */ for (; *isa && *isa != '_'; ++isa) if (unlikely(!isalnum(*isa))) ext_err = true; - /* Parse backwards */ + ext_end = isa; if (unlikely(ext_err)) break; + if (!isdigit(ext_end[-1])) break; - /* Skip the minor version */ + while (isdigit(*--ext_end)) ; - if (tolower(ext_end[0]) != 'p' - || !isdigit(ext_end[-1])) { - /* Advance it to offset the pre-decrement */ + + if (tolower(ext_end[0]) != 'p' || !isdigit(ext_end[-1])) { ++ext_end; break; } - /* Skip the major version */ + while (isdigit(*--ext_end)) ; + ++ext_end; break; default: + /* + * Things are a little easier for single-letter extensions, as they + * are parsed forwards. + * + * After checking that our starting position is valid, we need to + * ensure that, when isa was incremented at the start of the loop, + * that it arrived at the start of the next extension. + * + * If we are already on a non-digit, there is nothing to do. Either + * we have a multi-letter extension's _, or the start of an + * extension. + * + * Otherwise we have found the current extension's major version + * number. Parse past it, and a subsequent p/minor version number + * if present. The `p` extension must not appear immediately after + * a number, so there is no fear of missing it. + * + */ if (unlikely(!isalpha(*ext))) { ext_err = true; break; } - /* Find next extension */ + if (!isdigit(*isa)) break; - /* Skip the minor version */ + while (isdigit(*++isa)) ; + if (tolower(*isa) != 'p') break; + if (!isdigit(*++isa)) { --isa; break; } - /* Skip the major version */ + while (isdigit(*++isa)) ; + break; } + + /* + * The parser expects that at the start of an iteration isa points to the + * character before the start of the next extension. This will not be the + * case if we have just parsed a single-letter extension and the next + * extension is not a multi-letter extension prefixed with an "_". It is + * also not the case at the end of the string, where it will point to the + * terminating null character. + */ if (*isa != '_') --isa;